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74 Cards in this Set
- Front
- Back
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Describe static electricity |
This is when two insulating materials are rubbed together and electrons are transferred from one object to the other so one of the objects has a positive static charge and the other has a negative static charge. Two of the same charge repel each other and so a build up on each material of the same charge means the particles repel eachother but are in fixed positions and cannot move. |
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In static electricity, what is it that moves? |
The electrons |
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What are the effects of static electricity? |
Attracting dust - dust particles are tiny and light weight so are easily attracted to anything charged meaning the ions attract it Clinging clothes and crackling - clothes are dragged over each other and scrape off electrons leaving static charges leading to attraction and little sparks as the charges rearrange themselves Bad hair - static builds up on your hair giving each strand the same charge so they repel eachother |
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What is electric current? |
A flow of charge |
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What is electric current measured in? |
Amperes |
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What happens to the charges in a circuit? |
The metal conductors are full of free electrons that can move so the battery pushes the electrons through the wires and they are not used up but flow in a continuous loop |
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Why doesn't charge flow through insulators? |
Because there are few charges free to move |
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What does an ammeter do? |
It's connected to a circuit to measure the flow of a current at a chosen point |
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What happens if a battery has a large voltage? |
The current increases |
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What transfers energy away from the charge? |
The component |
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What is a voltmeter and where should it be placed? |
It's used to measure potential difference between two points so must be placed parallel with a component so it can compare the energy the charge has before and after passing through the component |
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How does the current through a component vary with voltage across it when the resistance stays constant |
The current through a component is proportional to the voltage across it when the resistance stays constant - different resistors have different resistance (the steeper the line the lower the gradient) |
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Higher resistance equals? |
A higher temperature |
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How do filament lamps work? |
When electrons pass through resistors they collide with positive stationary ions in the resistor - this makes the ions vibrate which causes an increase in temperature. A filament lamp contacts wire with a really high resistance which means that when the current passes through it, the temperature increases so much that it glows |
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How do LDRs work? |
They change their resistance depending on the amount of light. Bright light means low resistance but darkness means high resistance |
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How do thermistors work? |
It changes its resistance depending on the temperature - if it's hot then resistance falls but if it's cool then resistance increases |
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What happens if the resistance increases? |
There is less current |
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The amount of current depends on what? |
There's a balance between the voltage which pushes the current and resistance which opposes it - it depends on their relative sizes |
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What parts of a circuit resists the flow of charge? |
The components The connecting wires but this is so small it can be ignored |
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What is power and what is it measured in? |
The rate at which a power supply transfers energy to an appliance |
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What happens when an electric charge flows through a component? |
Work is done by the power supply and energy is transferred to the applicants and or its surroundings |
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Give an example of a fixed resistor |
Filament lamp |
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Give an example of a variable resistor |
LDR and thermistor |
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What is potential difference? |
Another word for voltage. It's the amount of energy transferred to or from each unit of charge as it moves between two points Therefore also the work done on or by a charge |
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What transfers energy to the charge? |
The battery |
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In a series circuit, what happens to the potential difference? |
The potential difference across the components add up to the potential difference across the battery because the total work done on the charge by the battery must equal the total work done by the charge on the components |
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In a series circuit, what happens to the current? |
The current is the same everywhere |
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What about resistance in a series circuit? |
The total resistance is the sum of the individual resistances |
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Is the sum of two resistors in a series circuit bigger or smaller than the resistor on its own? |
Bigger resistance as the battery has to push charge through all of them |
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Where is the potential difference at its largest across a series circuit? |
Across the component with the greatest resistance as more work is done by the charge |
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What happens in a series circuit if there is a change in resistance in one component? |
It will result in the potential difference changing for all components |
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In a series circuit, what happens to the potential difference? |
The potential difference across the components add up to the potential difference across the battery because the total work done on the charge by the battery must equal the total work done by the charge on the components |
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Where is the current largest in a parallel circuit? |
Through the component with the smallest resistance - P.d is the same throughout so less resistance means more current |
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In a series circuit, what happens to the current? |
The current is the same everywhere |
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What about resistance in a series circuit? |
The total resistance is the sum of the individual resistances |
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Is the sum of two resistors in a series circuit bigger or smaller than the resistor on its own? |
Bigger resistance as the battery has to push charge through all of them |
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Where is the potential difference at its largest across a series circuit? |
Across the component with the greatest resistance as more work is done by the charge |
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What happens in a series circuit if there is a change in resistance in one component? |
It will result in the potential difference changing for all components |
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In a parallel circuit, what happens to potential difference? |
It's the same throughout as each component is equal to the potential difference of the battery |
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In a parallel circuit, what happens to current? |
Total current adds up - its shares between branches |
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In a parallel circuit, what happens to resistance? |
Total resistance is lower than that of the least resistant branch as it provides more paths for charges to move along so has less resistance and a higher current |
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In a parallel circuit is the current of a component the same as it would be in its own circuit? |
Yes as each component is separately connected to the battery |
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How does adding further cells affect a series circuit? |
The voltage increases The current stays the same |
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How does adding further cells affect a parallel circuit? |
The voltage stays the same The current increases but there's less current in each cell |
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What is the mains domestic supply and in what form? |
230 V and AC |
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How do transformers work? |
The primary coil induces a magnetic field in the iron core - because there's an alternating voltage the magnetic field of the core continuously changes which induces an alternating voltage in the secondary coil |
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Why is an AC supply used for mains electricity not DC? |
Because it's easier to generate and to distribute over long distances |
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What is DC and an example? |
The current always stays in the same direction Batteries |
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How is mains electricity produced? |
By generators using the process of electromagnetic induction |
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Explain electromagnetic induction |
You can create a voltage by moving a magnet in or near a coil of wire which changes the magnetic field of the coil of wire and so induces a voltage at the ends of the wire. If the ends of the wire are connected to a full circuit then a current will flow in the wire. |
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Describe how generators use electromagnetic induction |
In a generator a magnet rotates within a coil of wire - when the magnet does half a turn the direction of the coils magnetic field reverses therefore the voltage reverses and the current flows in the opposite direction. If the magnet keeps turning in the same direction the voltage reverses every half turn and you get an AC current |
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What does the direction of the voltage in electromagnetic induction depend on |
If you move the magnet in or out of the coil The pole that points into the coil - north or south |
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How can you increase the size of the induced voltage created by a generator? |
Add an iron core to strengthen the magnetic field Increase the speed of rotation Increase the strength of the magnetic field Increase the number of turns on the coil |
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What is a transformer? |
Two coils of wire wound on an iron core which can change the size of alternating voltage |
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What are the two types of transformer? |
Step up transformers - they increase voltage so there are more turns in the secondary coil Step down transformers - they decrease voltage so there are more turns on the primary coil |
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What is the mains domestic supply and in what form? |
230 V and AC |
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How do transformers work? |
The primary coil induces a magnetic field in the iron core - because there's an alternating voltage the magnetic field of the core continuously changes which induces an alternating voltage in the secondary coil |
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What does bending a current carrying wire do? |
The magnetic fields around the side of the wire reinforce eachother at the centre |
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As a current carrying wire has a magnetic field, this means that what? |
It can exert a force on a permanent magnet or on another current carrying wire or coil |
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What happens if a current carrying wire is placed in a magnetic field at a right angle to the lines of force? |
The wire experiences a force at right angles to both the current direction and the lines of force of the field |
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What if a current carrying wire is placed parallel to the lines of force of a magnetic field? |
It experiences no force |
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What is Flemings left hand rule |
First finger = field SeCond finger = Current ThuMb= Motion |
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What is the motor effect? |
When a rectangular coil of wire carrying a current is placed between a uniform magnet field and the force causes it to turn |
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What is the split-ring commutator? |
It swaps the contacts every half turn which reverses the direction of current every half turn and so let's the coil rotate continuously in the same direction. Otherwise the direction of force would change every half turn so that it could not fully rotate |
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How are motors used? |
You can stick anything to a motor axle and make it spin around so it's in Domestic appliances DVD players Hard disk drive Electric motor vehicles |
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Why is an AC supply used for mains electricity not DC? |
Because it's easier to generate and to distribute over long distances |
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What is DC and an example? |
The current always stays in the same direction Batteries |
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How is mains electricity produced? |
By generators using the process of electromagnetic induction |
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Explain electromagnetic induction |
You can create a voltage by moving a magnet in or near a coil of wire which changes the magnetic field of the coil of wire and so induces a voltage at the ends of the wire. If the ends of the wire are connected to a full circuit then a current will flow in the wire. |
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Describe how generators use electromagnetic induction |
In a generator a magnet rotates within a coil of wire - when the magnet does half a turn the direction of the coils magnetic field reverses therefore the voltage reverses and the current flows in the opposite direction. If the magnet keeps turning in the same direction the voltage reverses every half turn and you get an AC current |
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What does the direction of the voltage in electromagnetic induction depend on |
If you move the magnet in or out of the coil The pole that points into the coil - north or south |
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How can you increase the size of the induced voltage created by a generator? |
Add an iron core to strengthen the magnetic field Increase the speed of rotation Increase the strength of the magnetic field Increase the number of turns on the coil |
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What is a transformer? |
Two coils of wire wound on an iron core which can change the size of alternating voltage |
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What are the two types of transformer? |
Step up transformers - they increase voltage so there are more turns in the secondary coil Step down transformers - they decrease voltage so there are more turns on the primary coil |
