What is the difference between the circuit symbols for a fixed resistor and a variable resistor ?

The symbol for a variable resistor has an arrow going through it, whereas the symbol for a fixed resistor does not. The resistance of a variable resistor can be adjusted , but the resistance of a fixed resistor is constant .

How should an ammeter and a voltmeter be connected in a circuit?

Ammeters are always connected in series . Voltmeters are always connected in parallel .

What is the function of a fuse in a circuit?

A fuse protects expensive components from current surges and acts as a safety measure against fire .

Name three functional components and state what each does when current passes through it.

Motors rotate Lamps emit light Heaters transfer thermal energy

Define generator . (Extended Tier Only)

A generator is a device which produces current . A d.c. generator is a source of direct current and an a.c. generator is a source of alternating current .

In which direction does current flow through a diode ? (Extended Tier Only)

Current can only flow through a diode in one direction . This is the direction that the triangle points in the circuit symbol.

Why can an LED be used to indicate the presence of a current in a circuit? (Extended Tier Only)

An LED illuminates when current flows through it in the correct direction, so it gives a visual response to the presence of a current.

True or False? Current is different at different points in a series circuit.

False. Current is the same value at any point in a series circuit.

True or False? The amount of current flowing in a series circuit depends on the voltage of the power source and the resistance of the components in the circuit.

True. The amount of current flowing in a series circuit depends on the voltage of the power source and the resistance of the components in the circuit.

If the voltage of the power source is increased, but everything else in the circuit remains constant, what effect does this have on the current ?

If the voltage of the power source is increased, but everything else in the circuit remains constant, more current is driven around the circuit, so the current will increase .

If the voltage of the power source remains constant, but more components are added to the circuit, what effect does this have on the current ?

Adding components to the circuit increases the total resistance of the circuit, so the current will decrease (for a constant voltage).

True or False? In a parallel circuit, the current from the power source is larger than the current in each branch.

True. The current splits along each branch at a junction, so the current from the source is larger than the current in each branch.

True or False? One advantage of a parallel circuit is that each lamp can be arranged in its own branch with its own switch.

True. In a parallel circuit, lamps can be switched off and on individually without breaking the whole circuit.

True or False? One advantage of a series circuit is that if one component stops working the others will still work.

False. An advantage of parallel circuits is that if one bulb breaks, the rest continue to function, as current passes along each branch independently. If one component fails in a series circuit, then the circuit is broken and the current cannot flow.

True or False? Current is conserved at a junction in a parallel circuit. (Extended Tier Only)

True. The current flowing into the junction is equal to the current flowing out of it. This is because charge is conserved.

True or False? Current always splits equally at a junction in a parallel circuit. (Extended Tier Only)

False. Current will only split equally at a junction if the resistance of the components along each branch is identical .

What is the rule for potential difference in a series circuit? (Extended Tier Only)

In a series circuit, the sum of the potential differences across the components is equal to the total e.m.f. of the power supply.

What is the rule for potential difference in a parallel circuit? (Extended Tier Only)

The potential difference across each branch of a parallel circuit is the same as the e.m.f. of the power source.

If one branch of a parallel circuit contains multiple components, what happens to the potential difference across that branch? (Extended Tier Only)

The potential difference across the branch is split between the components on that branch.

What is the rule for calculating the combined resistance of two or more components in series?

When two or more components are connected in series , the combined resistance is equal to the sum of the individual resistances .

True or False? The combined resistance of two resistors in parallel is less than that of either resistor by itself.

True. When resistors are connected in parallel , the combined resistance is less than the resistance of any of the individual components.

True or False? If two resistors of equal resistance are connected in parallel, the combined resistance will halve.

True. If two resistors of equal resistance are connected in parallel, the combined resistance is half the value of each individual resistor.

Why does a resistor heat up when an electric current passes through it?

When a current passes through a resistor , energy is transferred to heat due to the collisions of the free electrons within it, so its temperature increases . Some of this energy is dissipated into the surroundings by heating.

What hazard does damaged insulation on a wire pose?

Exposed wires can cause electric shocks if touched.

What hazard does the overheating of cables pose?

Overheating of cables could cause the insulation to melt , or even cause a fire .

Why is it dangerous to use electrical circuits in damp conditions?

Water is an electrical conductor , so moisture touching a live wire could set up a short circuit within the device (which could cause a fire) or a conductive path for current to flow through a person to the earth, causing electrocution .

Why is it dangerous to overload plugs, extension leads and multiple sockets when using the mains supply?

Overloading the mains supply can cause an excessive current to flow. The heat created could cause the insulation to melt , or even cause a fire .

Name four safety features built into domestic electrical appliances.

Safety features built into domestic appliances include: double insulation earthing fuses circuit breakers (trip switches)

What does it mean for an appliance to be double insulated ?

A double insulated appliance has two layers of insulation: insulation around the wires themselves a non-metallic case that acts as a second layer of insulation Double insulated appliances do not require an earth wire .

Why does the casing of an electrical appliance have to be either non-conducting or earthed?

The casing of an electrical appliance must be either non-conducting or earthed to prevent the casing from becoming electrified and causing an electric shock to anyone who touches it.

How does the earth wire make an appliance safe if a live wire touches its metal case?

The earth wire provides a low resistance path to the earth . This causes a surge of current in the earth wire and hence also in the live wire. The high current causes the fuse to melt and break , which cuts off the supply of electricity to the appliance, making it safe.

What is the purpose of a fuse?

A fuse is a safety device designed to cut off the flow of electricity to an individual appliance if the current becomes too large due to a fault or a surge.

How does a fuse stop the current when the current becomes too large?

The thin metal wire inside the fuse heats up and melts . This causes the wire to break , breaking the circuit and stopping the current .

How do you choose the correct fuse rating for an appliance?

Choose the fuse with the value just above the current required by the appliance. Fuses come in values of 3 A , 5 A and 13 A , so an appliance using 3.1 A needs a 5 A fuse.

True or False? A fuse without an earth wire protects the circuit and the cabling for a double-insulated appliance.

True. A double-insulated appliance does not require an earth wire , but a fuse still protects the circuit and the cabling from excess current.

What is the function of a trip switch?

A trip switch is a switch on the consumer unit that automatically breaks the circuit if the current becomes too high.

What are the main advantages of trip switches?

Trip switches provide protection from current surges or faults , and they can be reset when the problem is fixed.

IGCSEScienceCambridge (CIE)Co-ordinated Sciences (Double Award)PhysicsFlashcards4. Electricity & MagnetismElectric Circuits & Electrical Safety

Electric Circuits & Electrical Safety (Cambridge (CIE) IGCSE Co-ordinated Sciences (Double Award): Physics): Flashcards

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What is the difference between the circuit symbols for a fixed resistor and a variable resistor?

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Cards in this collection (38)

What is the difference between the circuit symbols for a fixed resistor and a variable resistor?
The symbol for a variable resistor has an arrow going through it, whereas the symbol for a fixed resistor does not.
The resistance of a variable resistor can be adjusted, but the resistance of a fixed resistor is constant.
How should an ammeter and a voltmeter be connected in a circuit?
Ammeters are always connected in series.
Voltmeters are always connected in parallel.
What is the function of a fuse in a circuit?
A fuse protects expensive components from current surges and acts as a safety measure against fire.
Name three functional components and state what each does when current passes through it.
- Motors rotate
- Lamps emit light
- Heaters transfer thermal energy
Define generator. (Extended Tier Only)
A generator is a device which produces current.
A d.c. generator is a source of direct current and an a.c. generator is a source of alternating current.
In which direction does current flow through a diode? (Extended Tier Only)
Current can only flow through a diode in one direction.
This is the direction that the triangle points in the circuit symbol.
Why can an LED be used to indicate the presence of a current in a circuit? (Extended Tier Only)
An LED illuminates when current flows through it in the correct direction, so it gives a visual response to the presence of a current.
True or False?
Current is different at different points in a series circuit.
False.
Current is the same value at any point in a series circuit.
True or False?
The amount of current flowing in a series circuit depends on the voltage of the power source and the resistance of the components in the circuit.
True.
The amount of current flowing in a series circuit depends on the voltage of the power source and the resistance of the components in the circuit.
If the voltage of the power source is increased, but everything else in the circuit remains constant, what effect does this have on the current?
If the voltage of the power source is increased, but everything else in the circuit remains constant, more current is driven around the circuit, so the current will increase.
If the voltage of the power source remains constant, but more components are added to the circuit, what effect does this have on the current?
Adding components to the circuit increases the total resistance of the circuit, so the current will decrease (for a constant voltage).
True or False?
In a parallel circuit, the current from the power source is larger than the current in each branch.
True.
The current splits along each branch at a junction, so the current from the source is larger than the current in each branch.
True or False?
One advantage of a parallel circuit is that each lamp can be arranged in its own branch with its own switch.
True.
In a parallel circuit, lamps can be switched off and on individually without breaking the whole circuit.
True or False?
One advantage of a series circuit is that if one component stops working the others will still work.
False.
An advantage of parallel circuits is that if one bulb breaks, the rest continue to function, as current passes along each branch independently.
If one component fails in a series circuit, then the circuit is broken and the current cannot flow.
True or False?
Current is conserved at a junction in a parallel circuit. (Extended Tier Only)
True.
The current flowing into the junction is equal to the current flowing out of it.
This is because charge is conserved.
True or False?
Current always splits equally at a junction in a parallel circuit. (Extended Tier Only)
False.
Current will only split equally at a junction if the resistance of the components along each branch is identical.
What is the rule for potential difference in a series circuit? (Extended Tier Only)
In a series circuit, the sum of the potential differences across the components is equal to the total e.m.f. of the power supply.
What is the rule for potential difference in a parallel circuit? (Extended Tier Only)
The potential difference across each branch of a parallel circuit is the same as the e.m.f. of the power source.
If one branch of a parallel circuit contains multiple components, what happens to the potential difference across that branch? (Extended Tier Only)
The potential difference across the branch is split between the components on that branch.
What is the rule for calculating the combined resistance of two or more components in series?
When two or more components are connected in series, the combined resistance is equal to the sum of the individual resistances.
True or False?
The combined resistance of two resistors in parallel is less than that of either resistor by itself.
True.
When resistors are connected in parallel, the combined resistance is less than the resistance of any of the individual components.
True or False?
If two resistors of equal resistance are connected in parallel, the combined resistance will halve.
True.
If two resistors of equal resistance are connected in parallel, the combined resistance is half the value of each individual resistor.
State the equation for calculating the combined resistance of two resistors connected in parallel. (Extended Tier Only)
The equation for the combined resistance of two resistors connected in parallel is
$\frac{1}{R} = \frac{1}{R_{1}} + \frac{1}{R_{2}}$
Where:
- $R$ = the combined resistance, measured in ohms (Ω)
- $R_{1}$ = the resistance of resistor 1, measured in ohms (Ω)
- $R_{2}$ = the resistance of resistor 2, measured in ohms (Ω)
Why does a resistor heat up when an electric current passes through it?
When a current passes through a resistor, energy is transferred to heat due to the collisions of the free electrons within it, so its temperature increases. Some of this energy is dissipated into the surroundings by heating.
What hazard does damaged insulation on a wire pose?
Exposed wires can cause electric shocks if touched.
What hazard does the overheating of cables pose?
Overheating of cables could cause the insulation to melt, or even cause a fire.
Why is it dangerous to use electrical circuits in damp conditions?
Water is an electrical conductor, so moisture touching a live wire could set up a short circuit within the device (which could cause a fire) or a conductive path for current to flow through a person to the earth, causing electrocution.
Why is it dangerous to overload plugs, extension leads and multiple sockets when using the mains supply?
Overloading the mains supply can cause an excessive current to flow. The heat created could cause the insulation to melt, or even cause a fire.
Name four safety features built into domestic electrical appliances.
Safety features built into domestic appliances include:
- double insulation
- earthing
- fuses
- circuit breakers (trip switches)
What does it mean for an appliance to be double insulated?
A double insulated appliance has two layers of insulation:
- insulation around the wires themselves
- a non-metallic case that acts as a second layer of insulation
Double insulated appliances do not require an earth wire.
Why does the casing of an electrical appliance have to be either non-conducting or earthed?
The casing of an electrical appliance must be either non-conducting or earthed to prevent the casing from becoming electrified and causing an electric shock to anyone who touches it.
How does the earth wire make an appliance safe if a live wire touches its metal case?
The earth wire provides a low resistance path to the earth. This causes a surge of current in the earth wire and hence also in the live wire. The high current causes the fuse to melt and break, which cuts off the supply of electricity to the appliance, making it safe.
What is the purpose of a fuse?
A fuse is a safety device designed to cut off the flow of electricity to an individual appliance if the current becomes too large due to a fault or a surge.
How does a fuse stop the current when the current becomes too large?
The thin metal wire inside the fuse heats up and melts. This causes the wire to break, breaking the circuit and stopping the current.
How do you choose the correct fuse rating for an appliance?
Choose the fuse with the value just above the current required by the appliance. Fuses come in values of 3 A, 5 A and 13 A, so an appliance using 3.1 A needs a 5 A fuse.
True or False?
A fuse without an earth wire protects the circuit and the cabling for a double-insulated appliance.
True.
A double-insulated appliance does not require an earth wire, but a fuse still protects the circuit and the cabling from excess current.
What is the function of a trip switch?
A trip switch is a switch on the consumer unit that automatically breaks the circuit if the current becomes too high.
What are the main advantages of trip switches?
Trip switches provide protection from current surges or faults, and they can be reset when the problem is fixed.

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