BMAT Physics Flashcards
1
Q
How do you charge an insulator?
A
- When two insulating material are rubbed together electrons will be scraped off one, leaving a positive electrostatic charge and a negative electrostatic charge on the other
- Friction
2
Q
Which object becomes negatively charged?
A
Object gaining electrons
3
Q
Which object becomes positively charged?
A
Object losing electrons
4
Q
What are the forces between charged objects?
A
- Attraction
- Repulsion
- Like charges repel, opposite charges attract
5
Q
What are the uses and dangers of electrostatics with paint spraying?
A
- Car manufacturers can save money by using charged paint spray guns
- They work because like charges such as positive and positive repel, and unlike charges such as positive and negative attract
- The spray gun is charged positively, which causes every paint particle to become positively charged
- Like charges repel and the paint particles spread out 5.The object to be painted is given a negative charge and so attracts the paint particles
- The advantages of using this system are that less paint is wasted, the object receives an even coat and the paint covers awkward ‘shadow’ surfaces that the operator cannot see.
6
Q
What are the uses and dangers of electrostatics with dust extraction?
A
- Smoke particles pick up a negative charge
- Smoke particles are attracted to the collecting plates
- Collecting plates are knocked to remove the smoke particles
7
Q
What is a conductor and insulator of electric current?
A
- Conductor: Charge is carried by negatively charged electrons e.g. copper wire
- Insulator: stops current flowing e.g. plastic
8
Q
What does a voltmeter and ammeter do?
A
- Voltmeter: measures voltage in a circuit
- Ammeter: measures current in a circuit
9
Q
What is the equation for resistance?
A
Voltage / Current
10
Q
What is the V-I graph like for a fixed resistor and a filament lamp?
A
- Fixed resistor: straight line, current thought a resistor at a constant temperature is proportional to voltage
- Filament lamp: as temperature of the metal filament increases, the resistance increases, hence the curve
11
Q
What is the current like in a parallel circuit?
A
- Each component in parallel has the same current as it would have if it were connected to the battery without the other components present
- This means that a higher resistance in parallel with a smaller resistance would have less current in it, as the same voltage will cause less current in a larger resistance than in a smaller one
- The current entering and leaving a branching point is equal
- Current on a single branch is the same
- Current on two different branches can differ
12
Q
What is the voltage like in a parallel circuit?
A
- The voltage across each component is the same as the voltage of the battery
- Voltage in each brach the same
13
Q
What is the current like in series circuit?
A
Same current flows through all parts of the circuit
14
Q
What is the voltage like in a series circuit?
A
The pd across resistors in series must add up to the battery voltage
15
Q
How do you calculate resistors in series?
A
Rt = R1 + R2
16
Q
What is the equation for voltage?
A
Energy / Charge
17
Q
What is the equation for power?
A
Current x voltage
18
Q
What is the equation for energy transfer?
A
Power x time = VIt
19
Q
What is the relationship between the number of turn of the primary and secondary coils and voltage ratio?
A
Vp / Vs = np / ns
20
Q
What is the consequence of a 100% efficiency of a transformer?
A
-Total transfer of electrical power, and that this gives rise to:
VpIp = VsIs
21
Q
When does electromagnetic induction occur?
A
When a wire moves relative to a magnet or when a magnetic field changes
22
Q
What is a generator?
A
A coil rotating in a magnetic field
23
Q
What is the equation for speed?
A
Distance / Time
24
Q
What is the difference between speed and velocity?
A
- Speed: is how fast you are going (scalar - magnitude only)
- Vector: how fast you are going with a direction (vector - magnitude and direction)
25
What is the equation for acceleration?
change in velocity / time
26
What is Newton's first law?
- The velocity of an object will not change unless a resultant force acts on it
- A body will stay still or move in a straight line at a constant speed, unless a resultant force acting on it
27
What is inertia?
The tendency of an object to to stay at rest or in motion
28
What is the equation for momentum?
mass x velocity
29
What is the conservation of momentum?
momentum before collision = momentum after collision
30
What is Newton's second law?
- If there is an unbalanced force, then the object will accelerate in that direction
- Force = mass x acceleration
31
What is the resultant force?
Fr = F1 + F2
32
What is the difference between mass and weight?
- Mass is the 'amount of stuff' in an object
- Weight is caused by the pull of gravity, a force
- W = mg
33
What is the gravitational field strength?
10 N/Kg on Earth
34
What is free-fall acceleration?
- A free falling object is an object that is falling under the sole influence of gravity
- Any object that is being acted upon only by the force of gravity is said to be in a state of free fall. There are two important motion characteristics that are true of free-falling objects:
1. Free-falling objects do not encounter air resistance.
2. All free-falling objects (on Earth) accelerate downwards at a rate of 9.8 m/s/s
35
What is terminal velocity and the forces involved?
1. The accelerating force acting on all falling objects is gravity and it would make them all accelerate at the same rate if it wasn't for air resistance
2. Air resistance causes things to fall at different speeds and the terminal velocity of any object is determined by its drag compared to its weight
3. The drag depends on its shape and areas
36
How does terminal velocity work with a human skydiver?
- Without his parachute he has a quite small areas and a force equal to his weight pulling him down
- He reaches terminal velocity at a very high speed, but with the parachute open there is much more air resistance and still only the force pulling hi, down
- This means that his terminal velocity comes down to a much smaller speed, which is a safe speed to hit the ground
37
What is Newton's third law?
If object A exerts a force on object B, then object B exerts and equal but opposite force on object A
38
What is the calculation for work?
Work = force x distance moved in direction of force
39
What is work done?
Transfer of energy
40
What is potential energy?
Mgh
41
What is kinetic energy?
0.5mv^2
42
What is a calculation for power?
Energy transfer / time
43
How are crumple zones used in road safety?
Crumple on impact, increasing the time taken for the car to stop so the force acting is smaller reducing injury
44
How are seat belts and air bags used in road safety?
- Safety Belts: stretch slightly, increasing the time taken for the wearer to stop and this reduced the forces acting on the chest
- Air Bags: slow you down more gradually
45
What is the law of conservation of energy?
Energy can never be created or destroyed it is only ever transferred from one form to another
46
What are some forms of energy?
electrical energy, light, sound, kinetic, nuclear, thermal. GPE, EPE, chemical
47
Wehn is energy useful?
Energy is only useful when it canoe transferred from one form to another
48
How do you calculate percentage efficiency?
useful output / total input x 100
49
What are thermal conductors and insulators?
- Thermal conductor: aluminium, iron
- Thermal insulator: wool, bedding
- Conduction is the process where vibrating particles pass on their extra kinetic energy to neighbouring particles
50
What factors affect the rate of conduction?
1. Temperature Difference (greater, greater rate of thermal energy transfer)
2. Length (longer, less heat successfully transferred)
3. Cross sectional area (greater, greater)
4. Material (thermal conductivity of the material per unit thickness)
5. Time (greater, greater )
51
How temperature affect the density of fluid?
- Hot water, less dense
| - Cooler water, more dense
52
How does convection currents work?
1. Heat energy is transferred from he heater coils to the water by conduction
2. The particles near the coils get more energy so start moving around faster
3. Particles further apart so becomes less dense
4. Reduction in density, means that hotter water tends to rise above the denser, cooler water
5. As the hot water rises it displaces the colder water out of the way, making it sink towards the heater coils
6. This water is then heated by the coils and rise and so it goes on. You end up with convection currents going up round and down, circulating the heat energy through the water
53
What factors affect the rate of convection?
1. Exposed surface area: greater, greater
2. Viscosity
3. Density
4. Conductivity: When conductivity is high, there is no need for convection
5. Acceleration due to gravity
54
What is heat radiation?
- Infrared radiation
| - Consists purely of EM waves of certain range of frequencies
55
What is absorption and emission?
1. Hotter object: emits more radiation than it absorbs (as it cools down)
2. Cooler object than its surroundings:absorbs more reaction than it emits (and warms up)
- Objects are continually emitting and absorbing radiation
56
What factors affect rate of absorption/emission?
- Surface area: larger, higher rate
- Volume and material
- Temperature difference
- A perfect black body is an object than absorbs all of radiation incident on it (does not reflect or transmit nay reaction)
- A good absorber is a good emitter
- Colour and texture: dull and black are better absorbers and emitters of IR than shiny white surfaces
57
What do waves do?
Transfer energy without met movement of matter
58
What is a transverse wave?
A wave where the direction of energy transferred is perpendicular to the direction of vibrations
59
What is a longitudinal wave?
A wave where the direction of energy transferred is parallel to the direction of vibrations
60
What are examples of waves ?
- Transverse: ripples on water, EM waves, seismic 'S' waves
| - Longitudinal: sound waves, seismic 'P' waves
61
What is the amplitude of a wave?
Height of the wave from the undisturbed position (rest to crest)
62
What is the wavelength of a wave?
Distance from one peak to the next
63
What is the frequency of a wave?
How many complete waves there are per second
64
What is the period of a wave?
The time it takes from one complete wave to pass a point
65
How do you calculate frequency?
1/ t
| 1Hz means one wave per second
66
How do you calculate wave speed?
frequency x wavelength
67
How do you know is a transformer is step up or step down?
1. Step Up: N2/N1 > 1
| 2. Step Down: N2/N1 < 1
68
What is reflected wave?
angle of incidence = angle of reflection
69
What is a refracted wave?
Change speed and direction moping through a different medium
70
What is diffraction?
Spreading out fo waves as they mass through a wave
71
What is the Doppler effect?
1. When the spruce is travelling towards you, the wavelength decreases and frequency increases
2. When the wave is travelling away from you the wavelength increases and the frequency decreases
72
What is the effect of reflection and refraction on speed frequency and wavelength?
hdhfghsd
73
Describe sound waves
-Reflection causes echoes (reflected signal)
-Ultrasound is sound with a frequency greater than 20,000 Hz
-Humans cannot hear ultrasound but many other animals can, such as mice, dogs and porpoises.
-Ultrasound is useful because it has a short wavelength so it can be focussed into a beam
Uses of ultrasound: scanning, sonar, animals
-This is due to the fact that ultrasound can be transmitted through soft tissue, but is mostly reflected when it comes into contact with more dense material such as bone
-Any ultrasound that is not reflected will be absorbed by the body
-Doctors also use ultrasound to monitor blood flow and destroy kidney stones
74
What are the properties of EM waves?
1. Can all travel at the speed of light in a vacuum
2. All transverse waves
3. All can be reflected, refracted and diffracted
75
What is the order of the electromagnetic spectrum?
- Radio waves, microwaves, infrared radiation, visible light, ultraviolet, X ray, gamma rays
- Decreasing wavelength, increasing frequency
- Know applications of EM waves
76
What are the dangers of EM waves?
- Intense sources of microwaves can be dangerous through internal heating of body cells
- The heating effect of IR can cause burns to the skin
- Ultraviolet light in sunlight can cause the skin to tan or burn
- Ultraviolet waves, X-rays and gamma rays are types of ionising radiation
- Ultraviolet waves can cause damage to skin cells and eyes, and increase the risk of skin cancer
- X-rays and gamma rays can cause the mutation of genes, which can lead to cancer
77
What are some popular models of atomic structure?
- Plum Pudding model
| - Rutherford Scattering Model
78
What is ionisation caused by?
A gain or loss of electrons
79
What is an isotope?
An atom of the same element with a different number of neutrons but the same atomic number
80
What is atomic number?
Number of protons in an atom of an element
81
What is atomic mass?
The number of neutrons and protons in an atom
82
What is radioactive decay?
- It is a spontaneous and random event
- Unstable nuclei decay
- Produce ionising radiation
83
What is alpha emission?
- 2 protons and 2 neutrons are decayed
- They stop quickly and don't penetrate far
- Strongly ionising
- Decreases atomic number by two and increases mass number by four
- Helium nuclei
- Slow moving
- Transmutes atom into a different element
84
What is beta emission?
- A electron emitted from the nucleus of an atom when a neutron turns into a proton and an electron
- When a beta particle is emitted, the number of protons in the nucleus increases by 1
- Penetrate moderately and are moderately ionising
- Transmutes atom into a different element with an atomic number plus one
- Moderately fast moving
85
What is gamma emission?
- Short wavelength EM waves
- No mass just energy
- Weakly ionising and penetrate a long way, fast moving
- Has no effect on atomic or mass numbers of the isotope
- Nucleus changes from a higher to a lower energy state
- Emits a high energy photon
86
What are radioactive emissions blocked by?
1. Alpha: paper, skin or few centimetres in air
2. Beta: stopped by thin metal (aluminium)
3. Gamma: blocked by thick lead or very thick concrete
87
What are the existence and origins of background radiation?
1. Substances of Earth: comes from air, food, building material, soil rocks
2. Radiation from space (cosmic rays): come mostly from the sun
3. Living things: there is a little bit of radioactive material in all living things
4. Radiation due to human activity e.g. fall out from nuclear explosions or nuclear waste (though this is usually a tiny proportion of the total background radiation)
- Cosmic rays, rocks, animals, soil and plants
88
What are the applications, dangers and hazards of ionising radiation?
- Sterilisation
- Kill cancerous tumours
1. Alpha: topical radiotherapy, smoke detector
2. Beta: medical tracers, checking paper thickness
3. Gamma: Sterilisation of equipment, radiotherapy, detecting damaged pipes
89
What is half life?
- The time taken to reduce the number of radioactive particles in half
- Decrease in activity over time
90
Describe nucelar fission?
- Caused by absorption of neutrons
- The nucleus of the atom splits into smaller parts
- Chain reaction: each time U235 nucleus splits, small number of neutrons which go on to hit other U235 nuclei, causing them to split and release more neutrons, (chain reaction)
- When splits, two daughter nuclei which are light elements and these are usually radioactive as they have the 'wrong' number of neutrons in them
- Each nucleus splitting gives out a lot of energy, and this energy is in the from of kinetic energy of the fission products
- This energy can be converted to heat energy in the reactor, by collisions with other atoms
91
Describe nuclear fusion
- Fusion of hydrogen to form helium
- Two small light nuclei fuse to form a heavier nucleus
- High temperature and pressure
- In all nuclear reactions a small amount of the mass changes to energy. This may not seem like a lot of energy but this energy is a result of the fusion of only four hydrogen nuclei
