ALL PHYSICS NOATS FOR YR 8 Flashcards
LEARN PHYSICS
Why does a light bulb transfer energy to its
surroundings?
A bulb transfers energy to the surroundings by light waves and heating when a current flows through it because the filament wire gets hot.
Why does a light bulb get hot when a current
flows through it?
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.
Why are resistors useful components in
electric circuits?
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.
What is voltage?
Voltage can be thought of as a measure of the energy transferred to (or from) the electrons flowing in the circuit.
How is voltage measured? What does the
measurement tell you?
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.
How does the voltage across the battery
relate to the voltage across the components in
a series circuit?
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.
How do you build a circuit that enables you to
plot a graph of current against voltage?
https://docs.google.com/presentation/d/1ql-8-OEeWAwS7vjPjf0Dlv8ovr4MhQnDtqG0x3Wgj6w/edit#slide=id.p
What would the current voltage graph look
like for a resistor?
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.
What would the current voltage graph look
like for different resistors?
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.
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https://docs.google.com/presentation/d/1bOViVWsg7RbrNv9cPI40SvBtwxu8fX84kXMSk7ahMo/edit#slide=id.p
What is resistance measured in?
Resistance is measured in ohms (Ω)
How do you calculate the resistance of a
resistor?
Resistance = Voltage / Current (R = V/I)
What are the two types of charge, positive and negative?
There are two types of charge, positive and negative. You can make a plastic rod charged by rubbing it with a cloth.
What happens to charged objects when they are brought near each other?
Similarly charged objects repel each other. Oppositely charged objects attract each other.
What are the structures of an atom?
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.
How are protons neutrons and electrons different to each other?
Protons have a positive charge and neutrons have no charge.
Electrons are negatively charged.
Why does rubbing a plastic rod with a cloth caused it to become charged?
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.
What happens if we keep on charging up an object?
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.
What happens if you get an electric shock?
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.
What is an electrical current?
The movement of charged particles such as electrons is known as electric current.
How can you make electrical current flow in a circuit?
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.
Why are wires in circuits made out of metals?
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.
What energy transfers take place in a circuit and how quickly does it happen?
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.
How do you measure current and what is it you are actually measuring when you do so?
We measure current using an ammeter. When we measure current we are measuring the rate of flow of electrons.
What is the unit for current and what does it mean?
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.
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.
Does current change depending on where you measure it in a series circuit?
Current is the same everywhere in a series circuit.
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.
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.
What is resistance?
Resistance can be thought if as a measure of how difficult it is for electrons to move through a circuit.
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.
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.
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.
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.
What is the unit for acceleration?
The unit of acceleration is m/s/s (metres per second per second).
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
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
What forces act on a falling object?
Air resistance drags up and weight drags down.
What is terminal velocity?
A falling object will accelerate to start with but then reaches a steady speed that we know as terminal velocity.
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.
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.
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
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
