Electrical charge & current

Figure 2 shows circuit symbols for some electrical components.

A student connects a circuit to measure the current in a filament lamp.

The student uses:

• an ammeter

• a cell

• a filament lamp.

Draw a circuit diagram for a circuit the student could use to measure the current in a filament lamp.

You should use three of the circuit symbols from Figure 2.

Which component is the source of energy for the circuit?

Tick () one box.

There is a current of 1.5 A in the filament lamp for a time of 30 s.

Calculate the charge flow in the filament lamp.

Use the equation:

charge flow = current × time

The current in the filament lamp is 1.5 A when the potential difference across the filament lamp is 12 V.

Calculate the resistance of the filament lamp.

Use the equation:

Choose the unit from the box.

Figure 3 shows how the current varies with potential difference for the filament lamp.

Describe the relationship between potential difference and current for the filament lamp.

As the current in the filament lamp increases, the temperature of the filament lamp increases.

What happens to the resistance of the filament lamp as the temperature increases?

In most homes, filament lamps have been replaced with LED bulbs.

Table 1 shows information about a filament lamp and an LED bulb.

Explain the advantages of using LED bulbs instead of filament lamps.

You should include a calculation in your answer.

Figure 1 shows a circuit diagram. The circuit contains a battery and two lamps, X and Y.

How does the current in lamp X compare with the current in lamp Y ?

Tick (✓) one box.

Lamp X and lamp Y are not identical.

The potential difference across the battery is 4.5 V.

The potential difference across lamp X is 1.5 V.

Calculate the potential difference across lamp Y.

The current in lamp X is 1.2 A.

The potential difference across lamp X is 1.5 V.

Calculate the power of lamp X.

Use the equation:

power = potential difference × current

Calculate the resistance of lamp X.

Use the equation:

The current in lamp X is 1.2 A.

Calculate the charge flow through lamp X in 40 seconds.

Use the equation:

charge flow = current × time

The switch can be used to turn the lamps on and off.

Immediately after the lamps are switched on, the resistance of each lamp increases.

Why does the resistance of each lamp increase?

Tick (✓) one box.

Figure 1 is repeated below.

Lamp Y breaks.

What happens to lamp X ?

Give a reason for your answer.

Tick (✓) one box.

A gardener wanted to build an electrical circuit to monitor the temperature in a greenhouse.

Which symbol represents an electrical component with a resistance that decreases as its temperature increases?

Tick (✓) one box.

When the resistance of an electrical circuit decreases, the current in the circuit increases.

Complete the sentence.

Choose the answer from the box.

Electrical current is a flow of.

The gardener wanted to find how the resistance of the component varies with temperature.

Figure 4 shows the equipment used by the gardener.

The resistance meter displays the resistance of the component.

Plan a method the gardener could use to find how the resistance of the component varies with temperature.

Figure 5 shows how the resistance of the component varies with temperature.

Complete the sentence.

Choose the answer from the box.

The relationship between the temperature and the resistance of the component

is.

The temperature in the greenhouse changed from 10 °C to 30 °C.

Determine the change in resistance of the component between these temperatures.

Use Figure 5.

The gardener builds a circuit that switches a heater on when the greenhouse gets

too cold.

Use the Physics Equations Sheet to answer questions 04.6 and 04.7.

Write down the equation that links current (I), potential difference (V) and power (P).

The power of the heater is 2900 W.

The potential difference across the heater is 230 V.

Calculate the current in the heater.

The camera in a mobile phone uses an LED to provide light when taking a photograph. A student investigated how the potential difference across an LED varies with the current in it. Figure 9 shows the circuit used.

The student closed the switch. The voltmeter gave a reading of 5.0 V The ammeter gave a reading of 0 mA The LED did not emit any light. Explain how the student should have changed the circuit to make the LED emit light.

The student changed the circuit so that the LED emitted light. The current in the circuit was 290 mA The power of the LED was 0.98 W Calculate the potential difference across the LED. Use the Physics Equations Sheet. Give your answer to 2 significant figures.

A traditional camera uses a flash unit to provide light. Figure 10 shows a flash unit on a traditional camera.

The flash unit emits light from xenon gas in a fluorescent tube. What happens when a xenon atom emits light? Tick (✓) one box.

When the flash unit is used there is a mean potential difference of 200 V across the fluorescent tube. The flash of light lasts for 2.8 × 10^–4 s 1.4 J of energy is transferred. Calculate the mean current. Use the Physics Equations Sheet.

A filament lamp breaks if the electric current in the filament becomes too big.

What is the correct symbol for a filament lamp?

Tick (✓) one box.

What is meant by an electric current?

Tick (✓) one box.

A manufacturer investigated the maximum current value of some filament lamps.

Figure 6 shows the symbols for an ammeter, a battery and a variable resistor.

The manufacturer connected an ammeter, battery, filament lamp and variable resistor in series.

Draw a circuit diagram to show the manufacturer’s circuit.

Include the symbol for a filament lamp from Question 03.1

How could the manufacturer increase the current in the filament lamp?

Tick (✓) one box.

When the potential difference across a filament lamp was 0.75 V, the current in the filament lamp was 0.16 A.

Calculate the power of the filament lamp.

Use the equation:

power = potential difference × current

Write down the equation which links charge flow (Q), current (I) and time (t).

The manufacturer increased the current in the filament lamp to 200 mA.

Calculate the charge flow through the filament lamp in 15 s.

The manufacturer increased the current in the filament lamp from 200 mA.

The filament in the lamp broke when the current reached 320 mA.

How many times greater than 200 mA was the current at which the filament broke?

The manufacturer tested lots of filament lamps.

The current at which the filament lamps broke was 320 ± 60 mA.

What is the range of currents at which the filament lamps broke?

Tick (✓) one box.

A student investigated how the resistance of a wire varies with the length of the wire. Figure 1 shows the circuit used.

The symbols for the voltmeter and ammeter in Figure 1 are not complete. Complete the symbols for the voltmeter and ammeter in Figure 1.

Which variable is the independent variable? Tick (✓) one box.

Which variable is the dependent variable? Tick (✓) one box.

The student took repeat readings of potential difference for a 30 cm length of the wire. The readings were: 0.16 V 0.17 V 0.15 V

Calculate the mean potential difference.

The length of the wire was increased to 60 cm The current in the wire was 0.50 A The mean potential difference across the wire was 0.32 V

Calculate the resistance of the 60 cm length of wire. Use the equation:

Calculate the power dissipated in the 60 cm length of wire. Use the equation: power = potential difference × current

Calculate the charge flow when there is a current of 0.50 A in the wire for 17 s Use the equation: charge flow = current × time

Figure 2 is a sketch graph of the results.

The student repeated the investigation using a thicker wire made from the same metal. For the same length, the thicker wire has a lower resistance. Draw a line on Figure 2 to show how the resistance of the thicker wire varies

A designer made some shoes that have lights in them.

Each shoe has a switch which closes when a person puts their foot on the floor.

Figure 1 shows the circuit.

What is component X ?

Tick (✓) one box.

Complete the sentence.

Choose the answer from the box.

When the switch was closed, the current in component X was

the current in the resistor.

The designer tested how the number of cells affected the number of steps that could be taken before the lights stopped working.

Figure 2 shows the results.

Determine how many more steps could be taken when the number of cells was increased from 3 to 5

How could the designer check the repeatability of the results?

Tick (✓) one box.

When the potential difference across the resistor was 0.80 V, the current in the resistor was 0.020 A

Calculate the power dissipated by the resistor.

Use the equation: power = potential difference × current

Which other equation can be used to calculate the power dissipated by a resistor?

Tick (✓) one box.

What happens to the temperature of the resistor when there is a current in it?

There was a current of 0.020 A in the resistor for 180 seconds.

Calculate the charge flow through the resistor.

Use the equation:

charge flow = current × time

Some ceiling lights in the home are connected to the mains by a two-core cable.

Figure 6 shows a ceiling light.

Suggest why some ceiling lights do not have an earth wire.

Write down the equation that links charge flow, current and time.

There is a current of 2.95 A in one of the copper wires for 60 seconds.

Calculate the charge flow through the wire.

Use your equation from question 04.2

Figure 7 shows a current potential difference graph for a piece of copper wire.

Draw another line on Figure 7 for a wire with a different resistance.

Some fuses have a thin piece of copper that melts if the current is too large.

Draw the circuit symbol for a fuse.

Describe how the movement of the copper particles in the wire changes when copper melts.

Old copper wires are melted when they are recycled.

Calculate the energy needed to melt 500 kg of copper at its melting point.

Specific latent heat of fusion of copper = 200 kJ/kg

Use the Physics Equations Sheet.

A student built a circuit using filament lamps.

Sketch a current potential difference graph for a filament lamp on Figure 9

Figure 10 shows the circuit with two identical filament lamps.

Compare the currents I₁, I₂ and I₃

Calculate the charge that flows through the cell in 1 minute. Each filament lamp has a power of 3 W and a resistance of 12 Ω Write any equations that you use. Give the unit.

The student builds a different circuit. Figure 11 shows the circuit.

Explain how the readings on both meters change when the environmental conditions change.