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GCSE Flashcards > Physics Paper 1 & 2 > Flashcards

Physics Paper 1 & 2 Flashcards

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1
Q

Specific heat capacity

A

The amount of energy needed to raise the temperature of 1 kg of a substance by 1 degree celsius

change in thermal energy, J
mass, kg
specific heat capacity, J/kg °C
temperature change, °C


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2
Q

System

A

object or group of objects

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3
Q

Closed system

A

Energy cant be transferred in or out surroundings, so we can say KPE=GPE.

If there is less KE at bottom that GPE at top, its not closed system, energy is lost to surroundings by energy used (work done against) by friction, air resistance.

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4
Q
A

The temperature at which a solid converts into a liquid is called the melting point.

The temperature at which a liquid converts into a gas is called the boiling point.

Increasing temperature increases volume (in a flexible container)

Increasing temperature increases pressure (in a fixed volume container)

Increasing concentration increases pressure (in a fixed volume container)

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5
Q

conduction and convenction

A

Conduction- vibrating particles transfer energy to neighboring particles

Convenction- where particles move away from hotter to colder regions.

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6
Q

Energy stores KG OF CEMENT (ACRONYM)

A

Thermal-heat
Kinetic-moving
Gravitational- gravity
Elastic- stretch
Chemical-batteries,food
Magnetic-magnets
Electrostatic- shocks
Nuclear- breaking atoms apart

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7
Q

The store of energy in 1 system can be transferred to another system by: HERM

A

Mechanically (when a force moves through a distance), muscles

Electrically (when a charge moves through a potential difference)

Heating (because of a temperature difference)

Radiation (e.g. light, microwaves, sound)

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8
Q

Kinetic energy

A

kinetic energy, J
mass, kg
speed, m/s

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9
Q

Elastic energy

A

elastic potential energy, J
spring constant, N/m
extension, m

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10
Q

Gravitational energy

A

gravitational potential energy, J
mass, kg
gravitational field strength N/kg (9.8)
height, m

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11
Q

Power ( W )

A

Rate at which energy is transferred
power, W
energy J
time, s
work done, J

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12
Q

Thermal conductivity

A

The higher thermal conductivity, heat energy moves faster by conduction, eg metal .
Higher rate of energy Transfer
Cavity walls, double glazing , loaf installation

Thus if you want something to stay warm you surround it with a material with a low thermal conductivity.

To reduce thermal energy transferred from a warm house, the walls can be built thicker, so the energy must travel further before it is transferred to the outside.

Insulation helps reduce loss of heat / energy.

The greater the temperature difference, the more quickly energy is transferred

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13
Q

Ways of reducing unwanted energy transfers to surroundings

A

Lubrication (reducing friction)

Streamlining (reducing drag/ motion)

Insulation (prevents heat loss)

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14
Q

Where does wasted energy go?

A

Ends up in thermal store in surroundings

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15
Q

SHC Practical

A

Keep block on heatproof mat.

Measure mass of metal block or water using top pan balance.

Wrap insulation around the block to not reduce energy transfer to surroundings

Put the heater in water of hole in the block.

Put metal into other hole in the block.

Measure initial temp of substance using thermometer.

Turn heater on, start timer, and measure p.d and current using ammeter and voltmeter.

After set time, measure final temp and calculate change in temp

Calculate power by power = p.d x current

Calculate energy supplied to block by
energy = power x time

Rearrange SHC equation.

Connect heater to power supply on and start timer.

Measure temp of block every 10 mins

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16
Q

Describe the energy changes when ball is thrown upwards

A

Upwards : KE is converted to GPE
Peak: Max GPE, 0 KE
Downwards: GPE is converted to KE

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17
Q

Energy transfers for bungee jumper

A

When falling, GPE converted to KE
Cord tights, KE converted to EP
At lowest point, jumpers GPE is same as EP

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18
Q

Waste energy

A

Not used by device for its desired purpose

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19
Q

How can efficiency of radiator be improved?

A

Metal foils behind radiator to reflect heat back than being absorbed

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20
Q

Renewable energy

A

Will not run out, can be replaced.

Eg, bio fuel, wind, hydroelectric, geothermal, the tides, solar and wave energy.

No green house gases produced, less carbon dioxide released, less global warming.

Unreliable eg cant use solar panels at night, wind if no wind

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21
Q

Non renewable energy ( burn to generate electricity/heat in power stations )

A

Will run out, cant be replaced.

Eg fossil fuels (coal, oil and gas), nuclear fuel.

More carbon dioxide released, global warming
Acid rain, because of sulphur dioxide

Can produce large amounts of energy, cheap, can be used anywhere in country

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22
Q

Uses of these resources

A

Transport- Nuclear (energy released from nucleus), Coal (fuel to generate electricity), Gas, Oil, Biofuel (burn of plants/ biomass to produce energy)

Heating- Solar (producing heat generating electricity), geothermal (heat within earth)

Electricity- Tidal (energy powered by the ocean tides) , wave (energy form waves), Hydroelectric (electricity generated by moving water), Wind (power of the wind to generate electricity)

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23
Q

Good emitters of infrared

A

Black, as good absorbers are good emitters too.
White reflect visible light, Black absorb it.

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24
Q

Science

A

Science has the ability to identify environmental
issues arising from the use of energy resources but not always the power to deal with the issues because of political, social, ethical or economic considerations.

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25
Q

Circuit symbols

A

Look at Aqa specification

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26
Q

Current

A

Speed of flow of charge.

charge flow, C
current, A
time, s

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27
Q

Diode

A

Current only flows in 1 direction.

Resistance is very high in other direction, preventing current flow.

Useful for controlling flow of current.

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28
Q

Resistance

A

Decreases current flow

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29
Q

Ohmic conductor

A

Conductor which current and p.d are directly proportional.

This means that the resistance remains constant as the temperature is constant too.

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30
Q

Filament lamp

A

Not directly proportional

Filament gets hot, so resistance increases, more energy needed to push the current.

Not at same rate.

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31
Q

LDR ( light dependent resistor )

A

light increases, resistance falls
light decreases, resistance is high
Eg, automatic light

LEDS are extremely energy efficient source of light.

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32
Q

Thermistor (temperature dependent resistor)

A

temp increases, resistance drops
temp decreases, resistance goes up
Eg, temperature detectors

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33
Q

Potential difference

A

pushes current around.

how much energy each charge has.

potential difference is just a way to measure how much energy there is for electricity to move around.

potential difference, V
current, A
resistance, Ω

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34
Q

National Grid

A

Distributes electricity across the country.

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35
Q

Difference between charge and current

A

charge is like the magic inside particles, and current is like the flow of those particles (or cars) through a wire.

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36
Q

Step up , Step down transformer

A

Step up transformer

-is used to increase the voltage and reduce the current. Less current means less energy is lost.

Step-down transformer

-reduces the voltage from the transmission voltage to the safer voltage of 230 V for home use.

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37
Q

Parallel

A

-Current is shared
-The potential difference is same
-The total resistance of 2 resistors is less than the resistance of the smallest individual resistor.
1/R+ 1/R

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38
Q

Alternating and direct p.d

A

Direct current- direct flow of current
Alternating current- changes direction

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39
Q

Why adding resistors in series increases the total resistance whilst adding resistors in parallel decreases the total resistance?

A

The more resistors we add in parallel, the more ‘pathways’ the current has to go through, so more current can flow

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40
Q

Difference between series and parallel

A

Series circuits – all components are connected in line with each other.
Parallel circuits – the components are connected in separate loops.

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41
Q

Resistance 1 : Practical

A

Set up a ciruit using ammeter, battery, voltmeter,

Attach a length of resistance wire to a metre ruler using crocodile clips.

Attach a crocodile clip to one end (the zero end) of the wire.

The students vary the length of wire by moving this crocodile clip and record the length of wire, current and potential difference to calculate resistance.

longer wire, more resistance.

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42
Q

UKs main electricity supply

A

frequency - 50 Hz
voltage- 230 V

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43
Q

3 Wires

A

neutral wire – blue (0 V)
- completes the circuit.
live wire – brown (230V)
- carries the alternating p.d
earth wire – green and yellow (0 V)
- protects wire

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44
Q

Dangers of wire

A

The earth wire carries current to the ground
(literally, earth).
This makes circuits safer because if there is a fault, it conducts the current to the ground rather than making the appliance ‘live’, or you would get shock.

The live wire is the most dangerous one, since it is at 230 V.
It should never touch the earth wire, because this would make a complete circuit from your mains supply to the ground (earth). A shock or fire would be highly likely.

Even if a circuit is switched off, the live wire can still be dangerous.
If you touch it, you may complete a circuit between the live wire and the earth (because you’ll be standing on
the floor), so you get a shock.

Every bulb has a fuse connected to live wire, its designed to melt/ blow if there is a fault that causes high current.

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45
Q

2 factors the amount of energy transferred by an appliance depend on

A

-Power of appliance

-How long appliance is being used for

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46
Q

3 things that determine power of a circuit device

A

-p.d across the circuit

-current through circuit

-amount of energy transferred

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47
Q

Solid

A

Most density
Vibrate in a fixed arrangement

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48
Q

Liquid

A

Middle density
Irregular arrangement
Flow over each other.

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49
Q

Gas

A

Low density
No regular arrangement
Particles move freely, in any speed.

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50
Q

Sublimation

A

solid to gas

Deposition-gas to solid

Evaporation
liquid to gas

Melting
Solid to liquid

To melt of evaporate, energy/ heat must be supplied to overcome the electrostatic forces of attraction between particles.

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51
Q

Particles of matter

A

Changes of state are physical changes because the material recovers its original properties if the change is reversed.

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52
Q

Internal energy

A

-Energy is stored inside a system by the particles.
-The total kinetic energy and potential energy of all the particles that make up a system.

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53
Q

Density: Practical (Irregular)

A

Place the stone on the top pan balance and measure its mass.

Fill the displacement can until the water comes out of hole

Place a measuring cylinder under the pipe ready to collect the displaced water.

Carefully drop the stone into the can with string and wait until no more water runs into the measuring cylinder.

Measure the volume of the displaced water= volume of object

Use the measurements to calculate the density of the stone.

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54
Q

Density: Practical (water)

A

Place the measuring cylinder on the top pan balance and measure its mass.
Pour 50 cm3 of water into the measuring cylinder and measure its new mass.
Subtract the mass in step 1 from the mass in step 2. This is the mass of 50 cm3 of water.
Use the measurements to calculate the density of the water.

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55
Q

Density: Practical (Regular)

A

Use a ruler to measure the length (l), width (w) and height (h) of a steel cube.
Place the steel cube on the top pan balance and measure its mass.
Calculate the volume of the cube using (l × w × h).
Use the measurements to calculate the density of the metal.
OR
Use vernier callipers to measure the diameter of the sphere.
Place the metal sphere on the top pan balance and measure its mass.
Calculate the volume of the sphere using formula of sphere.
Use the measurements to calculate the density of the metal.

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56
Q

The increase in temperature depends on…

A
  • mass of the substance
    -the type of material
    -energy input to the system.
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57
Q

What happens when a change of state occurs

A

-Internal energy decreases/ increases
-Temperature is same

58
Q

Specific latent heat

A

-The amount of energy required to change the state of 1 kg of the substance with no change in temperature.

59
Q

Specific latent heat of fusion
Specific latent heat of vaporisation

A

Specific latent heat of fusion
- change of state from solid to liquid

Specific latent heat of vaporisation
- change of state from liquid to
vapour

60
Q

Particles in gases

A

Changing the temperature of a gas, held at constant volume, changes the pressure exerted by the gas.

61
Q

Electrons

A

The more energy electrons have, the further they are from the nucleus.

If an electron gains energy by absorbing electromagnetic radiation then they move further away from the nucleus.

They can also give off electromagnetic radiation (in the form of light waves) and as a result they move back closer to the nucleus.

62
Q

Radioactive decay

A

Some isotopes have unstable nucleus, so they give out radiation to become more stable.

Random process

used in medicine, agriculture.

63
Q

Activity

A

Rate at which an unstable nuclei decays.

Measured in becquerel (Bq)
1 Bq- 1 decay per second.

64
Q

Count rate

A

Number of decays recorded each second by detector.

Geiger Muller tube

65
Q

Ion

A

Electrons can be added or removed from an atom to create an ion.

66
Q

Isotopes

A

Atoms with the same number of protons but different numbers of neutrons.

67
Q

Repeatable and Reproducible

A

Repeatable- same results

Reproducible- someone else gets same pattern

68
Q

Atoms electron arrangement when it emits EM radiation

A

Electrons are closer to nucleus
Lower energy level

69
Q

Nucleur radiation

A

Alpha
Beta
Gamma
neutron

70
Q

Alpha (α) (4,2)

A

2 protons, 2 neutrons

Same as helium nucleus

Range of alpha particle through air- few cm (5 cm)

Stopped by paper

Strongly ionising ( produce lots of ions when they collide with material )

Weakly penetrating

Smoke detectors–> smoke binds to ions, current stops and make noices

71
Q

Beta (β) (0, -1)

A

a high speed electron ejected from the nucleus (-1)

a neutron turns into a proton

Thin sheets of aluminium will stop beta.

Travel 15 cm in air before stopping.
Moderately ionising

Used to test thickness of sheets of metal.

72
Q

Gamma (γ) (0,0)

A

electromagnetic radiation from the nucleus ( no charge)

Weakly ionising as they pass through rather than collide.

Thick sheets of lead will stop gamma.

Several metres in air before stopping.

Getting rid of excess energy from nucleus.

Highly penetrating

73
Q

Half life

A

Time it takes for the
number of unstable nuclei of the isotope in a sample to halve.

74
Q

Contamination

A

Presence of unwanted radioactive isotope on other materials.

Dangerous, as the radioactive atoms decay and emit ionising radiation.

Radiation dose- sieverts (Sv)

75
Q

Irradiation

A

Exposing an object to ionising radiation
Material doesn’t become radioactive, as the object only comes in contact with the radiation not radioactive isotope.
Increase risk of cancer.

76
Q

Shielding

A

Gloves- alpha radiation
Lead apron- beta and gamma
Lead walls and glass containing lead- more dangerous.

77
Q

Radioactive Contamination

A

Alpha radiation: Strongly ionising but easily stopped by dead cells on the skin surface. Alpha emitters can be dangerous if inhaled or swallowed.

Beta radiation: Quite ionising and can penetrate skin into the body.

Gamma radiation: Weakly ionising. Can penetrate body but likely to pass straight through.

78
Q

Atoms

A

1 × 10-10

The radius of a nucleus is less than 1/10 000 of the radius of an atom.

79
Q

Model of an atom

A

Before the discovery of the electron, atoms were thought to be tiny spheres that could not be divided.

The plum pudding model suggested that the atom is a ball of positive charge with negative electrons embedded in it.

Alpha particle scattering experiment led to the conclusion that the mass of an atom was concentrated at the centre (nucleus) and that the nucleus was charged.

Niels Bohr adapted the nuclear model by suggesting that electrons orbit the nucleus at specific distances.

Later experiments led to the idea the name proton was given to these particles.

The experimental work of James Chadwick provided the evidence to show the existence of neutrons within the nucleus.

80
Q

Scalar and Vector quantities

A

Scalar
-have magnitude only.
Eg, distance, speed, mass, and time.
Vector
- have magnitude and direction.
Eg, force, velocity, displacement, and acceleration.

81
Q

Force

A

A push or pull that acts on an object due to the interaction
with another object.

82
Q

Contact forces and non-contact forces

A

Contact forces
- the objects are physically touching
eg, friction, air resistance, tension
Non-contact forces
- the objects are physically separated.
eg, gravitational force, electrostatic
force and magnetic force.

83
Q

Weight ( newtons )

A

Weight is the force acting on an object due to gravity.
Weight is measured using a calibrated spring-balance (a
newtonmeter).

84
Q

Resultant force

A

A single force that is equivalent to all the other forces acting on an object.

85
Q

Work done

A

1 joule = 1 newton-metre

86
Q

Elastic deformation and
Inelastic deformation

A

Elastic
if it returns to its original shape once the forces are removed,.
Inelastic
If it does not return to its original shape

87
Q

Newton’s First Law

A

An object remains in same state of motion unless resultant force is acted upon it

88
Q

Newton’s Second Law

A

force (N)= mass (kg) × acceleration (m/s2)

89
Q

Newton’s Third Law

A

For every action, there is an equal and opposite reaction

90
Q

Stopping distance

A

Thinking distance (driver’s reaction time) + braking distance ( distance it travels under the braking force)

91
Q

What affects a drivers reaction time (thinking distance)?

A

Tiredness
Drugs
Alcohol
Distractions

92
Q

What affects braking distance?

A

Road conditions
Poor tyre conditions
Poor brake conditions

93
Q

Energy transfers in cars

A

When a force is applied to the brakes, work done by the friction force between the brakes and the wheel reduces the kinetic energy of the vehicle and the temperature of the brakes increases.

The greater the speed of a vehicle the greater the braking force
needed to stop the vehicle in a certain distance.

The greater the braking force the greater the deceleration of the
vehicle. Large decelerations may lead to brakes overheating and/or
loss of control.

94
Q

Momentum

A

momentum (kg m/s) = mass × velocity
Momentum before=Momentum after

95
Q

Safety features of car

A

Seatbelts
Crample zone
Airbag
- increases time taken for momentum to reach 0, reduces force

96
Q

Waves

A

transfer energy without transferring matter

97
Q

Transverse waves

A

Vibration of wave is perpendicular to direction
Eg, light, electromagnetic waves
up and down

98
Q

Longitudinal

A

Vibration of wave is parallel to direction.
Eg, sound
side to side

99
Q

2 parts of longitudinal waves

A

Compressions and rarefractions

100
Q

Wave speed

A

Speed at which the wave moves.
m/s

101
Q

Amplitude

A

The maximum displacement of a point
on a wave away from its undisturbed position.

102
Q

Wave length

A

Length of one complete wave.

103
Q

Time period

A

Time taken for one wave to pass

104
Q

Frequency

A

no. of waves passing each second.
Hertz

105
Q

Waves practical

A

To measure the frequency, wavelength and velocity of waves in a ripple tank.

Set up equipment:

Adjust the bar so that its just touches the surface of the water.
Adjust motor to produce low frequency wave.
Adjust the lamp until the pattern in scan clearly on the screen

Frequency
* use a stopclock
* count the number of waves passing a point in a fixed time
period eg 10 seconds
* divide by 10
* f = 1/T
* read the frequency off the oscillator

Wavelength
* use a camera to freeze the image
* use a metre rule to measure the distance between two
wavefronts
* count the number of waves between the wavefronts
* divide distance by the number of waves to determine λ

Velocity
* determine a mean value of frequency
* determine a mean value of wavelength
* measure the time it takes one wavefront to travel the length of the screen
* measure the length of the screen
* speed = distance / time

106
Q

Reflection

A

Wave bounces off a surface.
waves can change direction when they change speed.

107
Q

Refraction

A

Waves changing direction at boundary.

108
Q

How waves travel in solids

A

Particles vibrate, and transfer kinetic energy through material.

109
Q

Electromagnetic waves

A

Transverse waves.
can travel through vaccum
do not need a medium to travel in

110
Q

EM spectrum

A

Radio waves—- Long wavelength,Low frequency
Microwaves
Infra red
Visible light
Ultra violent
X-rays
Gamma rays—Short wavelength, High frequency

111
Q

Examples ( raw meat is very unsanitary eXcept giraffe)

A

Radio waves- TV, Radio
Microwaves- cooking, communicate with satellites, as microwaves can pass through atmosphere without being reflected, refracted
Infra red- cooking, remote controls, infra red cameras, heat surroundings.
Visible light- vision, photography, only one detected by eye, tv signals, optical fibres, short wavelength, can carry alot of info.
Ultra violent- tanning, skin cancer, skin aging, more energy bc of shorter wavelength
X-rays- medical scans, absorbed by bone
Gamma rays- sterilising, medical treatment, detect cancer, penetrative, pass through body tissues

112
Q

Radiation dose

A

sievert (Sv)

113
Q

How can radio waves be produced

A

Vibrations in electrical circuit can produce radio waves, which one absorbed by a conductor, it produces an alternating current.
The alternating current has the same frequency as the radio waves so information can be quoted for transmission

114
Q

Why are X-rays and Gamma rays dangerous?

A

ionising radiation, causes mutation to genes, increased risk of cancer.

Hazard effects on human body tissue.

If energy of wave is high enough, it can cause an electron to leave its atom, leaving an ion, UV, X rays and gamma rays are ionising radiation.

115
Q

Dangers of EM Waves

A

Low frequency- Pass through soft tissue
High frequency- transfer alot of energy

116
Q

How to measure speed of sound?

A

Oscilloscope

117
Q

All waves can be…

A

Absorbed
Transmitted
Reflected
except gamma rays, they are emitted from nucleus.

118
Q

How are waves produced?

A

EM waves are produced when electrons lose energy.
electrons change energy levels

119
Q

IV Characteristics

A

-Ensure that the power supply is set to 0 at the start.
-Record the reading on the voltmeter and ammeter
-Use the variable resistor to alter the potential difference.
-Record the new readings on the voltmeter and ammeter.
-Repeat steps 2 and 3, each time increasing the potential difference slightly.
-Reverse the power supply connections and repeat steps 1-5
-Plot a graph of current against potential difference for each
component.
-Repeat the experiment but replace the fixed resistor with a bulb.

120
Q

Force: Practical

A

How mass changes acceleration, constant force.
Use the metre ruler to measure out intervals on the bench. Draw straight lines with pencil or chalk
Attach the bench pulley to the end of the bench
Put a 200 g mass on the car
Tie some string to the toy car or trolley. Attach the mass hanger to the other end of the string
Make sure the string is horizontal and is in line with the toy car or trolley
Select a weight to put on the weight hanger that will gently accelerate the car along the bench.
Hold the car at the start point
Release the car at the same time as you or a partner start the stopwatch.
Repeat steps 5-8 for increasing mass on the car.

121
Q

Force and acceleration: Practical

A
122
Q

4 examples of magnetic materials

A

Iron
Cobalt
Nickel
Steel (is an alloy which contains iron, so it is also magnetic)

123
Q

Magnets

A

The poles of a magnet are the places where the magnetic forces are strongest.

When two magnets are brought close together they exert a force on each other.

Two like poles repel each other.
Two unlike poles attract each other.

Attraction and repulsion between 2 magnetic poles are examples of non-contact force.

124
Q

There are two types of magnets

A

Permanent magnets

-produces its own magnetic field.
-always a magnet

Induced magnets

-material that becomes a magnet when it is placed in a magnetic field.
-Induced magnetism always causes a force of
attraction. When removed from the magnetic field an induced magnet loses most/all of its magnetism quickly.

125
Q

Magnetic field

A

The region around a magnet where a force acts on another magnet or on a magnetic material.

126
Q

Magnetic field

A

The strength of the magnetic field depends on the distance from the magnet.

The field is strongest at the poles of the magnet.

The direction of a magnetic field line is from the north (seeking) pole of a magnet to the south(seeking) pole of the magnet.

more closer the lines, the stronger the magnetic field.

127
Q

Describe how to plot the magnetic field pattern of a magnet using a compass

A

Place the plotting compass near the magnet on a piece of paper.
Mark the direction the compass needle points.
Move the plotting compass to many different positions in the magnetic field, marking the needle direction each time.
Join the points to show the field lines.

Compass will show direction of magnetic field, north to south.

When not near magnet, compass will point north - south, this is because the earth generates its own magnetic field, the earths magnetic field is due to the earths core.

128
Q

Direction of magnetic field

A

You just need to give a thumbs up on your right hand!

LOOK AT PICTURES IN GOOGLE DOC

129
Q

Increasing the strength of magnetic field by solenoid:

A

Increase the number of coils of the solenoid​

Increase the current​

Add an iron core in the middle of the solenoid

130
Q

Describe how the magnetic effect of a current can be demonstrated

A

The direction of this field is dictated by the ​’Right-hand Grip Rule’. ​

Plotting compasses on a piece of paper with a wire running through it

131
Q

Electromagnet (solenoid containing iron core)

A

Electromagnets are extremely useful as we can change the strength of the magnetic field by changing the size of the current

We can also turn an electromagnet on or off

When a wire has current flowing through it, magnetic field is produced around the wire.

The strength of this field can be increased by wrapping the wire into a coil named solenoid.

Electromagnet- a magnet where magnetic field can be turned on or off with electric current, meaning you stop the current.

To increase field strength of solenoid even more , add block of iron in centre of coil. The iron core becomes an induced magnet when current is flowing.

132
Q
A

We can prove it as a magnetic field around the wire by using a compass, when the current is turned off then the compass needle lines up with the earth’s magnetic field however if we turn the current on again then the compass needle deflect, this proves that there’s a magnetic field around the wire

133
Q

strength of the magnetic field

A

a larger current produces a stronger magnetic field

the magnetic field is also strongest closer to the wire as we move further from the wire the strength of the magnetic field decreases

if we change the direction of the current then we change the direction of the magnetic field

coil the wire- solenoid

134
Q

Fleming’s Left-Hand Rule

A

thumb- father, force
index- mother, magnetic field (N TO S)
middle-child, current (+ TO -)

135
Q

Magnetic Flux Density (strength of magnetic fields)

A

The number of lines of magnetic flux in a given area.
Measured in Tesla (T)

magnetic field lines = magnetic flux density

Higher magnetic flux density, stronger magnet, greater force

A stronger magnet will have a higher magnetic flux density. more lines are closer together

SEE DOCS

136
Q

Motor effect

A

When a conductor carrying a current is placed in a magnetic field , the magnet producing the field and the conductor exert a force on each other, causing wire to move.

To experience full force, the wire has to be at 90 degrees, if conductor is parallel, magnetic field will not experience a force

The strength of force, increases, with strength of magnetic field.

Force also increases with amount of current passing through conductor.

137
Q
A

Force = magnetic flux density x current x length​

N                      T                            A               m
138
Q

Factors Affecting Force on Conductor

A

Current: The larger the current, the larger the force.

Length: The longer the length of the conductor, the larger the force.

Magnetic Flux Density : The higher the density, the more magnetic field lines and the larger the force on the conductor.

139
Q

Electric motors

A

A wire carrying a current, both current in opposite directions, in a magnetic field tend to rotate.
This is the basis of an electric motor.

140
Q

Electric motor

A

current in the left-hand side of the coil causes a downward force, and current in the right hand side of the coil causes an upward force;
the loop of wire rotates anticlockwise because of the forces are in opposite directions.

Once loop is at 90 degrees, it stops rotating.

We use split-ring commutator (split metal ring), allows motor to keep rotating in same direction

a split ring commutator changes the current direction every half turn

The direction of rotation of the coil can be reversed by:

reversing the direction of the current OR
reversing the direction of the magnetic field (changing over the north and south poles).
The speed of rotation of the coil can be increased by:

increasing the size of the current;
using a stronger magnet;
increasing the number of turns of wire in the coil;
reducing
friction
between the coil and the axel it rotates on.

SEE IMAGE IN DOCS

141
Q

Solenoid

A

coil of wire
increase the strength of magnetic field by wrapping a wire into a coil.
the more closer field lines are , stronger the magnetic field

GCSE Flashcards (8 decks)

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