ALL PHYSICS NOATS FOR YR 8 Flashcards
LEARN PHYSICS (128 cards)
1
Q
Why does a light bulb transfer energy to its
surroundings?
A
A bulb transfers energy to the surroundings by light waves and heating when a current flows through it because the filament wire gets hot.
2
Q
Why does a light bulb get hot when a current
flows through it?
A
A bulb filament wire gets hot because electrons collide with the atoms inside it. These collisions happen because the filament wire has a property called resistance and we call the collision process resistive heating.
3
Q
Why are resistors useful components in
electric circuits?
A
A resistor is a useful component that can be used to keep the current at safe levels in a circuit and also to make heating devices e.g. in a kettle. This is because energy is transferred in a resistor in the same was as in a bulb; we can’t see the process as easily but they get hot too.
4
Q
What is voltage?
A
Voltage can be thought of as a measure of the energy transferred to (or from) the electrons flowing in the circuit.
5
Q
How is voltage measured? What does the
measurement tell you?
A
Voltage is measured using a voltmeter and its unit is the volt. The voltage measured can be related to the energy transferred to the component by the electrons or by the battery to the electrons. A higher voltage tells you more energy is transferred.
6
Q
How does the voltage across the battery
relate to the voltage across the components in
a series circuit?
A
The voltage across the battery equals the total voltage of all of the components. This is because the energy transferred to the electrons as they pass through the battery must equal the work done (energy transferred from them) as they pass through components.
7
Q
How do you build a circuit that enables you to
plot a graph of current against voltage?
A
https://docs.google.com/presentation/d/1ql-8-OEeWAwS7vjPjf0Dlv8ovr4MhQnDtqG0x3Wgj6w/edit#slide=id.p
8
Q
What would the current voltage graph look
like for a resistor?
A
It would be a straight line through the origin. This is because for a resistor voltage is directly proportional to current. This means if you double voltage you will double current.
9
Q
What would the current voltage graph look
like for different resistors?
A
A larger resistor will require more voltage to allow the same current to flow through it. Another way of thinking about this is that when the same current flows through a larger resistance more work will be done by the electrons (more energy transferred from them) and the voltage across it will be larger.
+
https://docs.google.com/presentation/d/1bOViVWsg7RbrNv9cPI40SvBtwxu8fX84kXMSk7ahMo/edit#slide=id.p
10
Q
What is resistance measured in?
A
Resistance is measured in ohms (Ω)
11
Q
How do you calculate the resistance of a
resistor?
A
Resistance = Voltage / Current (R = V/I)
12
Q
What are the two types of charge, positive and negative?
A
There are two types of charge, positive and negative. You can make a plastic rod charged by rubbing it with a cloth.
13
Q
What happens to charged objects when they are brought near each other?
A
Similarly charged objects repel each other. Oppositely charged objects attract each other.
14
Q
What are the structures of an atom?
A
An atom consists of a tiny central nucleus made up of neutrons and protons surrounded by electrons which orbit it. There are the same number of protons and electrons in an atom. The atom has no overall share.
15
Q
How are protons neutrons and electrons different to each other?
A
Protons have a positive charge and neutrons have no charge.
Electrons are negatively charged.
16
Q
Why does rubbing a plastic rod with a cloth caused it to become charged?
A
The movement of electrons is responsible for charging the rods; electrons are added (becomes negative) or take away (becomes positive) by the friction between the cloth and the r0d.
17
Q
What happens if we keep on charging up an object?
A
If we charge up an object negatively by continually adding electrons to it, there comes a point where the electrons won’t stay on the object and will jump off it directly down to the ground or to another object that is touching the ground . We see this movement of electrons as a spark.
18
Q
What happens if you get an electric shock?
A
If the electrons move off a very charged object to the ground through a person they will experience this movement of electrons and an electric shock.
19
Q
What is an electrical current?
A
The movement of charged particles such as electrons is known as electric current.
20
Q
How can you make electrical current flow in a circuit?
A
We can make electrons in the wires move by attaching a battery across a wire. The electrons move in the circuit because they experience a repulsive force from the negative terminal (and an attractive force from the positive terminal) of the battery.
21
Q
Why are wires in circuits made out of metals?
A
Metals are conductors because the electrons are free to move - some electrons don’t belong to any one particular atom like they do in insulators. The forces exerted on electrons from a typical battery are not enough to make them move in an insulator because they are very securely attached to an individual atom.
22
Q
What energy transfers take place in a circuit and how quickly does it happen?
A
In a simple battery/bulb circuit when a current flows the chemical store of the battery decreases and the thermal store of the bulb increases. This energy transfer happens as soon as the circuit is complete - there is no time delay.
23
Q
How do you measure current and what is it you are actually measuring when you do so?
A
We measure current using an ammeter. When we measure current we are measuring the rate of flow of electrons.
24
Q
What is the unit for current and what does it mean?
A
Current is measured in amperes (amps, A) and 1A is the equivalent of more than 6 trillion electrons flowing past a point in the circuit, and back to the battery.
25
What is a series circuit?
A series circuit is a simple circuit where there is only one route that electrons could take from the battery, through all the components, and back to the battery.
26
Does current change depending on where you measure it in a series circuit?
Current is the same everywhere in a series circuit.
27
What happens to current when a larger battery voltage is used?
Current increases when the battery voltage is increased. This is because the electrons experience stronger forces of attraction and repulsion to the terminals.
28
What happens to current when more bulbs are put into a circuit?
Current decreases when there are more bulbs. This is because more circuit components increases the resistance.
29
What is resistance?
Resistance can be thought if as a measure of how difficult it is for electrons to move through a circuit.
30
Why does a bulb get brighter when there is a larger current flowing through it?
A larger current increases the rate at which energy is transferred from the battery to the bulb. The bulb develops more power when a larger current flows through it.
31
What is an electromagnet?
If a wire is wrapped around an iron core, connected to battery, and then switched on a magnetic field is created. This arrangement is known as a solenoid.
32
How do you increase the strength of an electromagnet?
If you have more turns of wire wrapped round the iron core and if you increase the current flowing through the wires you will increase the strength of the electromagnet.
33
What is acceleration?
What is deceleration?
Acceleration is the rate at which an object speeds up.
Deceleration is the rate at which an object slows down.
34
What is the unit for acceleration?
The unit of acceleration is m/s/s (metres per second per second).
35
What does an acceleration of
1m/s/s mean?
An acceleration of 1 m/s/s tells us that every second an object’s speed increases by 1m/s
36
What does a speed time graph tell
us?What happens to an object when a
resultant force acts on it in the
direction it is moving?
A straight line tells us that the object is moving with constant acceleration. The steeper the line on a speed time graph the larger the object’s acceleration. A flat line on a speed-time graph tells us the object is moving at a constant speed.
37
What happens to an object when a
resultant force acts on it in the
direction it is moving?
When a resultant force acts on an object in the direction it is moving that object accelerates and its kinetic store increases.
38
What is the relationship between
the size of an object’s acceleration
and the resultant force acting on it?
The larger the resultant force acting on an object the larger that object’s acceleration. Acceleration is directly proportional to resultant force. This means that if resultant force doubles acceleration doubles.
39
What does a graph of acceleration
against resultant force look like?
A graph of acceleration against resultant force will be a straight line through the origin.
40
What happens to an object when a
resultant force acts on it in the
opposite direction to its motion?
When a resultant force acts on an object in the opposite direction to motion that object will decelerate, its kinetic store will decrease and the thermal store of the surroundings will increase.
41
When you push an object, and then
let go, why does it slow down?
The force you used to push the object is a contact force so as soon as the object is out of
your hands there is no longer any contact and therefore no push force. In the absence of
friction this object would keep on moving at a steady speed because there would be no
resultant force on it. In reality the object will slow down because there is a resultant force acting on it in the opposite direction to its motion; this is caused by friction between the object and the surface it is on.
42
How do we stop moving vehicles?
When we stop moving objects such as cars, we use the brakes to apply a force on the vehicle in the opposite direction to its motion.
43
Why do we stop moving vehicles
over a longer period of time?
We try to apply the braking force over a longer period of time because this means the
speed is reduced more slowly and this results in a smaller deceleration. Smaller
decelerations require smaller resultant forces.
44
Why do objects moving through air
experience air resistance?
When objects move through air there are air resistance forces that act on them because
the object collides with air molecules.
45
Why do larger surface areas and
faster speeds result in more air
resistance?
The larger the surface area of the object and the faster it is moving the more air
molecules it will collide with per second and the larger the air resistance force it will
experience.
46
What forces act on a falling object?
Air resistance drags up and weight drags down.
47
What is terminal velocity?
A falling object will accelerate to start with but then reaches a steady speed that we know as terminal velocity.
48
Why do falling objects reach
terminal velocity?
An object dropped from a height accelerates downwards to start with because its weight
is the only force acting on it and therefore there is a resultant force downwards. However, it will not accelerate forever as the air resistance force acting on it increases as it gets faster. This reduces the resultant force acting on the object and makes its acceleration smaller. Eventually the air resistance force will equal the weight and at this point there will be no resultant force so the object cannot accelerate any further –
the object has reached a steady speed known as terminal velocity.
49
What energy transfers take place in
an object falling at terminal
velocity?
An object falling at terminal velocity is losing height so its gravitational store is
decreasing however because it is not getting any faster its kinetic store doesn’t change.
The energy lost from its gravitational store is transferred to the thermal store of the
surroundings due to the work done by air resistance.
50
How do you calculate speed, distance or time if you
know two of them?
Speed can be calculated using the formula, speed = distance / time
Time can be calculated using the formula time = distance / speed
Distance can be calculated using the formula distance = speed x time
51
What is the unit for speed?
If distance is in metres and time in seconds then the unit for speed is m/s
If distance is in kilometres and time in hours then the unit for speed is km/h
52
What does a distance time graph tell us?
A straight line tells us the object is moving with constant speed. The gradient of a line on a
distance time graph tells us the speed. The steeper the line is on a distance time graph the
faster an object is moving. A flat line on a distance time graph tells us the object is
stationary.
53
What is a contact force?
A contact force occurs when two objects touch each other. Friction, normal contact force, and air resistance are examples of contact forces.
54
What is a non-contact force?
A non-contact force does not require two objects to touch each other. Gravitational and magnetic forces are examples of non-contact forces.
55
What is the normal contact force?
The normal contact force (sometimes known as reaction force) is the push up of the ground on the object in contact with it
56
What is a magnetic field?
A magnetic field is a region around a magnet where magnetic materials experience magnetic forces
57
What does the magnetic field around a bar magnet look like?
https://docs.google.com/presentation/d/1h67xOCkyumZMuzQnFzTEzzU64qUX_DNYV79hg7pDIk/edit#slide=id.p
58
What does a magnetic field diagram tell us?
How close the field lines are on a magnetic field diagram tell us how strong the field is
(closer the lines, stronger the field) and the direction of the arrows tells us the direction a
North pole would move in if you put it in the field.
59
How can you determine the shape of a magnetic field experimentally?
The shape of the field can be determined by using a plotting compass. Place the compass
near to the magnet and put a dot on the page next to where the needle arrowhead points.
Then place the compass so that the tail of the needle is on the dot and place a new dot
where the compass arrowhead now points. Repeat until you go off the page or back round
to the magnet. Join the dots up smoothly. Repeat for a different starting point.
60
What is the Earth’s gravitational field?
The Earth’s gravitational field is the region around the Earth where objects will experience
attractive forces towards the centre of the Earth.
61
How can you measure the gravitational force acting on an object?
Gravitational forces on objects can be measured by freely suspending the object from a newton meter and reading the scale.
62
How strong is the Earth’s gravitational field?
On the surface of the Earth the strength of the gravitational field is 10 N/kg. The Earth’s
gravitational field gets weaker as you move further above the surface.
63
How can you measure the Earth’s gravitational field strength?
Gravitational field strength can be determined by working out the gradient of a graph of
gravitational force against mass.
64
What is weight?
The gravitational force of attraction you experience because you are in the Earth’s
gravitational field is also known as your weight. Weight is a force and is measured in
newtons (N).
65
What is mass?
Mass is the amount of material that makes you up and is measured in kg.
66
How can you calculate an object’s weight?
Your weight on Earth can be calculated by using the following formula Weight = mass x 10
67
What are the rules for drawing force diagrams?
When drawing force diagrams force arrows should always start on the object; the size of
the arrow tells us the size of the force and the direction tells us which way the force acts.
68
What is a resultant force?
If two (or more) forces act on an object then these can be replaced by a single force arrow
that we call the “resultant force”.
69
How do you calculate the size of a resultant force?
If the forces act in the same direction we add the forces to work out the size of the
resultant force. If the forces act in opposite directions then we take the smallest one away
from the biggest to work out the size of the resultant force.
70
What is Newton’s first law?
Newton’s first law tells us that if no resultant force acts on an object then that object’s
motion will not change; it will either stay still or, if it is already moving, then it will carry on
moving at a steady speed. If there is a resultant force acting on an object then the object’s
motion will change.
71
What happens to an object’s motion if a resultant force acts on it?
A resultant force in the direction in which an object is moving will cause it to speed up. A
resultant force in the opposite direction to the way an object is moving will cause it to slow
down.
72
What is pressure?
The pressure under a solid object in contact with a surface is a measure of how spread out
the force is. The same force exerted over a larger area (e.g. wearing flat shoes) will result in
a lower pressure than if that force is exerted over a smaller areas (e.g. wearing high heals).
73
How do you calculate pressure?
Pressure can be calculated using the formula pressure = force / area.
74
What is the unit for pressure?
If force is measured in N and area in cm2 then the unit for pressure is N/cm2
75
What is energy?
Energy doesn’t have a definition. It is needed for things to happen but it doesn’t explain why
those things happen. When processes happen to an object there are changes in the amount of
energy stored in that object
76
What does the amount of
energy an object have depend
on?
The amount of energy an object has depends on: it’s temperature, it’s shape, it’s mass, it’s speed,
it’s height above the earth’s surface and how it’s atoms are arranged or combined
77
What is energy measured in?
The amount of energy something has is measured in joules (J)
78
What do we mean by a
thermal store of energy?
Thermal store: energy due to an object’s temperature. Thermal stores increase when the object gets hotter and decrease when it gets colder
79
What do we mean by an
elastic store of energy?
Elastic store: energy due to an object having a greater/shorter length than its natural length.
Elastic stores increase if the object is stretched or squashed from its natural shape and decrease if
it returns to its natural shape.
80
What do we mean by a kinetic
store of energy?
Kinetic store: energy due to an object’s mass and speed. Kinetic stores increase if an object’s
speed increases and decrease if an object is slowed down.
81
What do we mean by a
gravitational store of energy?
Gravitational store: energy due to an object’s height above the Earth’s surface. Gravitational
stores increase if an object is lifted up and decrease if it falls down.
82
What do we mean by a
chemical store of energy?
Chemical store: energy due to atoms combining in a chemical reaction.
83
How can you cause a change
in an object’s energy?
Changes in an object’s energy happen because of: forces doing work, a flow of an electrical
current, heating, light radiation, and sound waves
84
What do we mean when we
say a force does work?
When work is done by a force energy is transferred by that force
85
What are the energy transfers
involved in lifting something?
When a person lifts an object the work done by their force causes an increase in the gravitational
store of the object and a decrease in the person’s chemical store.
86
What are the energy transfers
involved when an object falls?
When an object falls from a height the work done by the force of gravity causes an increase in the
object’s kinetic store and a decrease in the object’s gravitational store.
87
What are the energy transfers
involved when a person pulls
an object at a steady speed?
When a person pulls an object at a steady speed their chemical store decreases but there is no
change in the object’s kinetic store. The force of friction between the object and the ground
causes the thermal store of the object and the ground to increase.
88
What are the energy transfers
involved when a battery
powers a light bulb?
When a battery is connected to a light bulb in an electrical circuit an electrical current flows. This
current causes the thermal store of the light bulb to increase and the chemical store of the
battery to decrease. When a light bulb is on it transfers energy to the surroundings by light
radiation and heating.
89
What are the energy transfers
involved when an ice cube is
left to melt?
When an ice cube is left on the kitchen table it’s thermal store increases because energy is
transferred from the surroundings to it by heating. The thermal store of the surroundings
decreases.
90
What is 1J?
1 joule of energy is transferred when a force of 1 Newton moves an object through 1 metre
91
How can you calculate the
amount of work done by a
force?
The amount of work done (energy transferred) by a force can be calculated using the formula
work = force x distance moved
92
What is power?
Power is the rate at which energy is transferred – this is a measure of how quickly energy is
transferred. Power is also the rate at which work is done.
93
What is power measured in?
Power is measured in watts. 1 watt is the same things as 1 joule per second (1W = 1 J/S)
94
How can power be calculated?
Power can be calculated using the formula power = energy transferred / time. Or power = work
done / time
95
What is the principle of
conservation of energy?
When an energy transfer happens energy is not created or destroyed. This is known as the
principle of conservation of energy.
96
What is dissipated energy?
When an energy transfer happens energy can be transferred usefully (what we want to happen)
but some energy is not transferred usefully (wasted) this is known as dissipated energy.
97
How do we see things?
We see any object because light from that object reaches the retina at the back of our eyes where
an electrical signal is then sent to our brain. Some objects are luminous and produce their own light, other objects reflect light from other sources.
98
What is the normal line?
The normal line is a dashed line drawn at 90 degrees to the surface of an object
99
What is the law of reflection?
The angle of incidence equals the angle of reflection
+
https://docs.google.com/presentation/d/1LBJn7acXNOGcoRqklQdlHdwDB_B6jCd971PziWUhW8/edit#slide=id.p
100
What is the difference between diffuse
and specular reflection?
Specular reflection happens when light is incident on smooth surfaces. Parallel rays of incident light are reflected in a predictable manner and remain parallel to each other upon reflection. Diffuse reflection happens on rough surfaces.Parallel rays of light do not remain parallel to each other on reflection and are scattered in different directions.
101
How can we draw a ray diagram to show
the formation of images in mirrors?
https://docs.google.com/presentation/d/1B37eA0ixgGQSf4NdOltQQY1lIIqjzA0CV2TvZacYDKk/edit#slide=id.p
102
What is a virtual image? Why is it
different to a real image?
A virtual image is one from which the light rays appear to come but don’t actually come from the
image e.g. the image seen in a mirror. A real image is one where the light rays do come from.
103
What is refraction and why does it
happen?
Refraction is the change in speed of a wave when it reaches the boundary between two different materials. It happens because materials have different densities. It causes the wave to change
direction.
+
https://docs.google.com/presentation/d/1hfGebxUYCD3naK9ghtPuD475JTSsKLbt2YsJPv0IuII/edit#slide=id.p
104
What effects does the refraction of light
lead to?
Refraction of light at water/air boundaries causes objects to appear closer to the water than they
actually are. Refraction is the reason why a straw in a glass of water looks “bent”.
105
What happens to parallel rays of light
when they enter a convex lens?
In a convex lens parallel rays of light are made to converge at a point known as the focal point.
+
https://docs.google.com/presentation/d/1oSlCG56eQa7Yub66pB79n9Z3aE37eDjOBvSUl05oPV0/edit#slide=id.p
106
What happens to parallel rays of light
when they enter a concave lens?
In a concave lens parallel rays of light are made to diverge away from the lens.
+
https://docs.google.com/presentation/d/179eF0vbUrR1vwMKk1PdhlNeFfQA1ZYG56LQigkxKAB4/edit#slide=id.p
107
How are lenses used to correct eye
defects?
Eye defects occur when the eye cannot focus light onto the retina. In shortsighted people the
incoming light is focused to a point before the retina. This can be corrected using a concave lens. In longsighted people the light would be focused on a point beyond the retina and this can be corrected using a convex lens.
108
What happens to white light when it is
shone through a prism?
When white light is shone through a prism the separate colours of the spectrum are seen. This is called dispersion and happens because different colour (wavelength) light changes speed by different amounts.
+
https://docs.google.com/presentation/d/1rlVEvFAR1oXx0vdb9ZSeO9NXfBQ4BT4vSww05S7i1E/edit#slide=id.p
109
What is the electromagnetic spectrum?
The electromagnetic spectrum is a family of transverse waves to which light belongs. They are
made when charged particles (e.g. electrons) are made to vibrate. The order of the electromagnetic spectrum from long wavelength to short wavelength is: Radio waves, Microwaves, Infrared, visible light, Ultra Violet, X-rays, and Gamma rays.
110
What are electromagnetic waves used
for?
Radio waves: Communication. Microwaves: Communication and cooking. Infrared: Heating and communication. Ultra violet: security and fluorescent lights. X-rays: medical imaging and cancer treatment. Gamma rays: medical imaging and sterilization.
111
Why are UV, X rays, and gamma rays
dangerous?
UV, x-rays and gamma rays can damage the structure of DNA within cells. This prevents the cell from replicating correctly and can lead to mutations and possible cancerous tissue.
112
What is a wave?
How is a wave created?
A wave transfers energy from one place to another without any overall transfer of matter.
In order to make a wave something needs to vibrate.
113
What is a transverse wave?
What waves are transverse?
In a transverse wave vibrations are at right angles (perpendicular) to the direction of energy
transfer (direction of the wave).
Waves on the surface of water (ripples) and light are two examples of transverse waves.
114
What is a longitudinal wave?
What waves are longitudinal?
In a longitudinal wave vibrations are in the same direction (parallel) as the direction of energy
transfer (direction of the wave).
Sound is an example of a longitudinal wave.
115
What is the definition of frequency?
What is its unit?
The frequency of a wave is defined as the number of vibrations per second (or the number of waves per second). Its unit is Hz (Hertz)
116
What is the definition of time period?
Time period is defined as the time for one vibration (or the time for one wave to pass a point).
117
What is the definition of amplitude?
The definition of amplitude is the maximum distance of a vibrating particle from its rest position.
118
What is the definition of wavelength?
The definition of wavelength is the distance from a point on a wave to the same point on the next
wave.
119
How do you label amplitude and
wavelength on a diagram of a wave?
https://docs.google.com/presentation/d/1BM4ziL_IwOeev5rk0Qrs7ElDpJjSk6ToG51O08xFFw/edit#slide=id.p
120
How is a sound wave produced?
A sound wave is produced when something vibrates.
121
What do sound waves do?
Sound waves (or sound radiation) transfer energy from the source of the sound (vibrating object) to our ears.
122
What happens to the particles in a
substance when a sound wave passes
through them?
Particles vibrate in a direction that is parallel to the direction of the wave. Sometimes particles are close together (compressions) and sometimes they are far apart (rarefaction)
+
https://docs.google.com/presentation/d/1VZUIkarprbN1u1mlbvdMThh8dD1017zWp6nHKooUKwM/edit#slide=id.p
123
Why can’t sound waves travel through a
vacuum?
A vacuum is a place where there are no particles at all. Space is a vacuum. Sound waves cannot
travel through a vacuum because particles need to vibrate in order for the energy transfer to take
place.
124
How can you demonstrate that sound
waves can’t travel through a vacuum?
You can demonstrate that sound waves can’t travel through a vacuum by putting a bell (or any
source of sound) into a strong glass jar that is connected to a vacuum pump. As the air particles
are removed from the jar by the pump the bell gets quieter. When all of the air particles have been removed the bell will be in a vacuum and is no longer heard.
125
How does a sound wave change when
sounds are louder or higher in pitch?
When a sound is made louder the amplitude of the wave increases. When a sound is a higher pitch the frequency of vibrations increases and time period decreases.
+
https://docs.google.com/presentation/d/1J7yxWT8Xr2AgUATpQIqLCQt7Mk005cjcdZzzFJDLS0o/edit#slide=id.p
126
What is the range of human hearing?
20Hz to 20,000Hz (20kHz)
127
What are sounds higher that 20kHz
known as? What are they used for?
Sounds with a higher pitch than 20kHz are known as ultrasound. Ultrasound can be used in medical imaging, medical treatments, and distance measurements and in industry.
128
How can you measure the speed of
sound?
Someone stood 100m away (measured with a tape measure) makes a visible sound (e.g. by
banging two blocks of wood together) and someone at the other end starts a stop clock when they see the sound being made and stops the stop clock when they hear it. Speed = distance / time. A more accurate way would be to use microphones and electronic timers because this removes all human reaction time.
