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Physics Flashcards

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1
Q

What happens when two objects interact

A

The forces they exert on each other are equal and opposite

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2
Q

What is a resultant force

A

When a number of forces acting at a point are replaced by a single force that has the same effect on the motion as the original forces all acting together

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3
Q

What can a resultant force acting on an object cause

A

A change in its state of rest or motion

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4
Q

What happens if the resultant force acting on an stationary object is zero

A

The object will remain stationary

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5
Q

What happens if the resultant force acting on an stationary object is not zero

A

The object will accelerate in the direction of the resultant force

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6
Q

What happens if the resultant force acting on a moving object is zero

A

The object will continue to move in at the same speed and in the same direction

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7
Q

What is the acceleration of an object determined by

A

The resultant force acting on the object and the mass of the object

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8
Q

What does the gradient of a distance-time graph represent

A

Speed

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9
Q

What is the velocity of an object

A

Its speed in a given direction

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10
Q

What does the gradient of a velocity-time graph represent

A

Acceleration

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11
Q

What happens when a vehicle travels at a steady speed

A

The resistive forces balance the driving force

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12
Q

The greater the speed of a vehicle …

A

The greater the braking force needed to stop it in certain distance

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13
Q

What are most resistive forces caused by

A

Air resistance

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14
Q

What is the stopping distance of a vehicle a sum of

A

The distance the vehicle travels during the driver’s reaction time (thinking distance)and the distance it travels under the braking force (braking distance)

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15
Q

What can a drivers reaction time be affected by

A

Tiredness
Drugs
Alcohol

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16
Q

What may affect driver’s ability to react

A

Distractions

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17
Q

What happens when the brakes of a vehicle are applied

A

Work done by the friction force between the brakes and the wheel reduces kinetic energy of the vehicle and the temperature of the brakes increases

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18
Q

What can a vehicles braking distance be affected by

A

Adverse road and weather conditions (wet and icy) and poor condition of the vehicle

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19
Q

The faster an object moves through a fluid …

A

… The greater the frictional force that acts on it

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20
Q

Why will an object falling through a fluid initially accelerate

A

The force of gravity. But eventually the resultant force will be zero and the object will move at its terminal velocity (steady speed)

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21
Q

What is the equation to calculate the weight of an object using the force exerted on it by a gravitational force

A

W = M * G

W = weight in newtons, N
M = mass in kg
G = gravitational field strength in newtons per kilogram, N/kg
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22
Q

What may a force acting on an object cause

A

A change in shape of the object

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23
Q

What will a force applied to an elastic object (e.g. a spring) result in

A

Stretching and storing elastic potential energy

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24
Q

For an object that is able to recover its original shape, where is elastic potential energy stored

A

In the object when work is done on the object to change its shape

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25
Q

What is the extension of an elastic object directly proportional to

A

The force applied, provided that the limit of proportionality is not exceeded

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26
Q

When is work done

A

When a force causes an object to move through a distance

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27
Q

How are work done, force and distance related by

A

The equation
W = F * D

W - work done in joules, J
F - force applied in newtons, N
D - distance moved in the direction of the force in metres, m

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28
Q

What is transferred when work is done

A

Energy

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29
Q

What is power

A

The work done or energy transferred in a given time
P = E/T

P - power in watts, W
E - energy transferred in joules, J
T - time taken in seconds, s

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30
Q

What is gravitational potential energy

A

The energy that an object has by virtue of its position in a gravitational field
Ep = m * g * h

Ep - change in gravitational potential energy in joules
M - mass in kg
G - gravitational field strength in newtons per kilogram, N/kg
H - change in height in metres, m

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31
Q

What does the kinetic energy of an object depend on

A

Its mass and its speed
Ek = 1/2 * m * v2

Ek - kinetic energy in joules
m - mass in kg
v - speed in metres per second, m/s

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32
Q

What is momentum

A

A property of moving objects
p = m * v

p - momentum in kilograms metres per second, kg m/s
m - mass in kg
v - velocity in metres per seconds, m/s

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33
Q

What is conservation of momentum

A

The total momentum before an event is equal to the total momentum after the event

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34
Q

What happens when certain insulating materials are rubbed against each other

A

They become electrically charged. Negative charged electrons are rubbed off on one material and onto the other

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35
Q

When is a material negatively charged

A

When it gains electrons

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36
Q

When does a material have an equal positive charge

A

When it loses electrons

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37
Q

What happens when 2 electrically charged objects are brought together

A

They exert a force on each other

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38
Q

When do objects repel

A

When they carry the same type of charge

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39
Q

When do objects attract

A

When two objects carry different types of charge

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40
Q

What kind of charges move easily through some substances e.g. metals

A

Electrical

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41
Q

What is electric current

A

A flow of electric charge

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42
Q

What is the size of the electric current

A

The rate of flow of electric charge

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43
Q

Equation for the size of current

A

I = Q/t

I = current in amperes, A
Q = change in coulombs, C
t = time in seconds, s
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44
Q

What is potential difference

A

Voltage

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45
Q

What is the potential difference between two points in an electric circuit

A

The work done (energy transferred) per coulomb of charge that passes between the points

V = W/Q

V - voltage
W - work done
Q - charge

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46
Q

What are current-potential difference graphs used to show

A

How the current through a component varies with the potential difference across it

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47
Q

What does a current-potential graph for a resistor at constant temperature look like

A

The current and voltage are in direct proportion

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48
Q

How can you measure the resistance of a component

A

Measuring the current through and the potential difference across the component

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49
Q

Equation for voltage

A

V = I * R

V - voltage
I - current
R - resistance

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50
Q

What does the current through a component depend on

A

It’s resistance

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51
Q

The greater the resistance …

A

…the smaller the current for a given potential difference across the component

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52
Q

What is the potential difference provided by cells connected in series the sum of

A

The potential difference of each cell (depending on the direction in which they are connected)

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53
Q

For components connected in series …

A

The total resistance is the sum of the resistance of each component
The current is the same in each component
The voltage is shared between the components

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54
Q

For components connected in parallel…

A

The potential difference across each component is the same

The total current through the whole circuit is equal to the current flowing through the separate components

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55
Q

The resistance of a filament bulb increases as …

A

…the temperature of the filament increases

56
Q

The current through a diode flows in …

A

…one direction only. The diode has a very high resistance in the reverse direction

57
Q

When does an LED emit light

A

When a current flows through it in the forward direction

58
Q

What is a LDR

A

Light-dependent resistor

59
Q

The resistance of a LDR decreases as …

A

… light intensity increases

60
Q

The resistance of a thermistor decreases …

A

… as the temperature increases

61
Q

What is direct current

A

Current that always passes in the same direction, cells and batteries supply this

62
Q

What is alternating current

A

One that’s constantly changing direction

63
Q

Which supply is the mains electricity

A

Alternating current

64
Q

What is the frequency and voltage of mains electricity in the UK

A

the frequency is 50 cycles per second (50 hertz) and is about 230 V

65
Q

How are most electrical appliances connected to the mains

A

Using cable and a three-pin plug

66
Q

What happens if an electrical fault causes too great a current

A

The circuit is disconnected by a fuse or a circuit breaker in the live wire

67
Q

What happens if the current in a fuse wire exceeds the rating of the fuse

A

It will melt, breaking the circuit

68
Q

What are some circuits protected by

A

Residual Current Circuit Breakers (RCCBs)

69
Q

How do RCCBs operate

A

By detecting a difference in the current between the live and neutral wires. They also operate much faster than a fuse

70
Q

Appliances with metal cases are usually …

A

… Earthed

71
Q

Some appliances are double insulated and therefore …

A

… Have no earth wire connection

72
Q

What do the earth wire and fuse protect

A

The wiring of the circuit

73
Q

What happens when an electrical charge flows through a resistor

A

The resistor gets hot

74
Q

What is power

A

The rate at which energy is transferred by an appliance
P = E/t

P = power in watts 
E = energy in joules
t = time in seconds
75
Q

How are power, voltage and current related by an equation

A

P = I * V

P - power in watts
I - current in amps
V - voltage in volts

76
Q

How are energy transferred, voltage and charge related by an equation

A

E = V * Q

E - energy in joules
V - voltage in volts
Q - charge in coulombs

77
Q

When is a substance radioactive

A

When they give out radiation from the nuclei of all their atoms all the time, whatever happens to them
Radioactive decay has a random nature

78
Q

What is an alpha particle

A

Helium nucleus - 2 neutrons and 2 protons

79
Q

What is a beta particle

A

An electron from the nucleus

80
Q

What is gamma radiation

A

A type of electromagnetic radiation

81
Q

What are types of background radiation

A

Natural sources:
Rocks
Cosmic rays from space

Man-made sources:
The fallout from nuclear weapons tests
Nuclear accidents

82
Q

What types of radiation are deflected by both electric and magnetic fields

A

Alpha and beta

Alpha particles are deflected less than beta particles because of its greater mass and in an opposite direction

83
Q

What type of field is gamma radiation deflected by

A

None

84
Q

What is a half-life of an radioactive isotope

A

The average time it takes for the number of nuclei of the isotope in a sample to halve
OR
the time it takes for the count rate from a sample containing the isotope to fall to half its initial level

85
Q

What are the 2 types of fissionable substances in common use in nuclear reactors

A

Uranium-235

Plutonium-239

86
Q

What is nuclear fission

A

The splitting of an atomic nucleus

87
Q

How does nuclear fission occur

A

The nucleus must first absorb a neutron
The nucleus undergoing fission splits into 2 smaller nuclei and 2 or 3 neutrons and their energy is released
The neutrons may go on to start to a chain reaction

88
Q

Nuclear fusion

A

The joining of the two atomic nuclei to form a larger one

89
Q

How is energy released in stars

A

Nuclear fusion

90
Q

Why do crumple zones and seatbelts work

A

Increases the time over which a crash occurs. This means the force is lower and less harm to driver/passengers

91
Q

Why can momentum be positive or negative

A

Because velocity can be in opposite directions

92
Q

Why will the momentum in opposite directions after an explosion or crash be the same size but different signs ( - or + )

A

The different directions

93
Q

What are protons and neutrons held together by

A

Strong forces which balances the repulsive electrostatic force between the protons

94
Q

When is a nucleus stable

A

When the electrostatic force is balanced

95
Q

What affects braking distance

A

Speed
Quality of brakes
Quality of tyres
How good the grip is (road surface, tyres, weather conditions)

96
Q

When an object falls, what is its potential energy converted into

A

Kinetic energy

Kinetic energy gained = potential energy lost

97
Q

What is the limit of proportionality

A

The maximum force that the elastic object can take and still extend proportionally

98
Q

What do brakes do

A

Reduce the kinetic energy by transferring it into heat (and sound)

99
Q

How are cars designed to convert kinetic energy safely in a crash

A

Crumple zones
Side impact bars
Seat belts
Air bags

100
Q

How do crumple zones help passengers in a car crash

A

Crumple up on impact
Converts car’s kinetic energy into other forms of energy as the car changes shape
Increase the impact time, decreasing force produced by momentum

101
Q

How do side impact bars help passengers in a car crash

A

Strong metal tubes fitted into car door panels

Help direct the kinetic energy of the crash away from the passengers to crumple zones

102
Q

How do seat belts help passengers in a car crash

A

Stretch slightly, increasing time taken for wearer to stop - reduces forces acting on chest
Stretching absorbs kinetic energy of the wearer

103
Q

How do air bags help passengers in a car crash

A

Slow you down more gradually

Prevent you from hitting hard surfaces in the car

104
Q

Diode

A

A special device made from semiconductor material e.g. silicon
Used to regulate the voltage in circuits
Lets current flow freely through it in only one direction

105
Q

When are parallel circuits used

A

In cars so everything can be turned on and off separately and gets the full voltage from the battery

106
Q

What can an oscilloscope screen show

A

Electricity supplies

107
Q

What does a DC source look like on an oscilloscope trace

A

A straight line as it is always at the same voltage

108
Q

What does an AC source look like on an oscilloscope trace

A

A regularly repeating wave. From that you can work out the period and frequency of the supply

109
Q

Equation for frequency

A

1/time period (s)

110
Q

What’s a time period

A

The time taken to complete a full cycle (peak to peak or trough to trough)

111
Q

Hazards in the home

A 
Long cables 
Frayed cables 
Cables in contact with hot or wet things 
Water near sockets
Damaged plugs 
Too many plugs in one socket 
Appliances without their covers 
Lighting sockets without bulbs in
112
Q

Live wire

A

Brown coloured

Alternates between +ve and -ve voltage

113
Q

Neutral wire

A

Always at 0V

Electricity flows in and out through the live and neutral wires only

114
Q

Earth wire

A

Protects the wiring

Works together with a fuse to prevent fire and shocks

115
Q

Why is the earth wire connected to the metal casing

A

So it can carry the electricity to earth should something go wrong and the live or neutral wires touch the metal case

116
Q

Wiring of plugs

A

Neutral wire - left pin
Earth wire - top pin
Live wire - right pin (attached to fuse)

117
Q

What do different appliances need

A

Different amounts of energy

Thicker cables have less resistance, so they carry more current

118
Q

What are metal parts of plugs made from and why

A

Copper or brass because they are very good conductors

119
Q

What is the case, cable grip and insulation made from and why

A

Rubber or plastic because they are really good insulators and flexible too

120
Q

What is ‘earthing’

A

When the case is attached to an earth wire

An earthed conductor can never become live

121
Q

When is an appliance double insulated

A

If it has a plastic casing and no metal parts showing

These don’t need an earth wire

122
Q

Two-core cables

A

Cables that only carry live and neutral wires

123
Q

Things affecting radiation dose

A

High altitude
Being underground
Working in mines or the nuclear industry
Working as a radiographer in hospitals

124
Q

Order of ionisation (most to least)

A

Alpha
Beta
Gamma

125
Q

Order of penetration (most to least)

A

Gamma
Beta
Alpha

126
Q

What happens when a beta particle is emitted

A

A neutron turns to a proton in the nucleus

127
Q

How do smoke detectors use alpha radiation

A

A weak source of alpha radiation is placed in the detector, next to two electrodes
The source causes ionisation and a current flows between the electrodes
If there’s a fire then smoke will absorb the radiation - so the current stops and the alarm sounds

128
Q

What type of isotopes can be taken into the body

A

Gamma or beta emitters so that the radiation passes out of the body
Ones with a short half-life so that the radioactivity inside the patient quickly disappears

129
Q

Which type of rays are used in radiotherapy

A

Gamma as they can kill all living cells

130
Q

Sterilisation of food and surgical instruments with radiation

A

Exposure to a high dose of gamma rays kills all microbes, keeping food fresher
Alternative to medical instruments being boiled
Irradiation doesn’t involve high temperature so fresh fruit and plastic can be sterilised without damage

131
Q

How are stars initially formed

A

Clouds of dust and gas, and the force of gravity makes the dust and gas spiral in together and produces a protostar. Temperature rises and pressure rises inside the star

132
Q

What’s the voltage of Earth

A

0V

133
Q

What does a neutron decay to

A

A proton and a beta particle

134
Q

Nebulae

A

Clouds of dust and gas

135
Q

Nuclear fusion vs. Nuclear fission

A

Fusion releases more energy
Less radioactive emissions
Uses ‘cleaner fuel’ (hydrogen)

Additional Science (3 decks)

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