Current, resistance and potential difference

What is an ammeter used to measure?

A Charge

B Current

C Potential difference

D Resistance

A student uses a small magnet to build an electric motor.

The magnetic field around the magnet can be shown like this:

The battery is connected to the coil of insulated wire by the metal pins.

The current is clockwise around the coil of insulated wire and part of the coil is perpendicular to the magnetic field.

State the technique used to find the direction of the force acting on the coil.

The table shows some data about the motor.

Calculate the force acting on the coil.

Use the Equation Sheet.

The student now doubles the number of coils in the motor.

They do this by using a piece of wire which is twice as long.

The battery, the wire diameter, the wire material and the coil size are unchanged.

The current in the original coil was 500 mA.

State the current in the new coil.

Explain whether the new motor turns faster, slower, or at the same speed as the original motor.

Consider the force acting on the new coil.

Some scientists are comparing the resistance of circuits.

Their first circuit contains one lamp, a cell, an ammeter, a voltmeter and some connecting leads.

Draw a circuit diagram to show how they should connect these components.

Diagram

The scientists build more circuits, each time adding one more lamp to their circuit.

The table shows their results.

Number of lamps	Potential difference across each lamp (V)	Total resistance in the circuit ()
1	6.0	5.0
2	6.0	3.8
3	6.0	3.3
4	6.0	2.9
5	6.0	2.6
6	6.0	2.4

Calculate the largest current through the cell observed by the scientists.

Use the equation: potential difference = current × resistance

Explain how the scientists connected the additional five lamps.

Use their results from the table. You can use a diagram.

Optional diagram

This question is about how electrical circuits work.

A student builds three different electrical circuits.

Explain why the lamp does not light in each circuit.

Fig. 12.1 shows the first circuit.

Fig. 12.1

The lamp does not light because........

Fig. 12.2 shows the second circuit.

Fig. 12.2

The lamp does not light because........

Fig. 12.3 shows the third circuit.

Fig. 12.3

The lamp does not light because........

The student uses the meters in the circuit in Fig. 12.4 to determine the resistance of a resistor.

Fig. 12.4

The student uses the circuit to take several readings of current and potential difference. The graph shows the student’s results.

Complete the sentence about the graph to explain the relationship between potential difference and current. Use words from the list.

decreases increases stays the same

As the potential difference increases, the current........

The ratio of potential difference: current at 3 V is 15: 1.

Calculate the ratio of potential difference: current at 6 V. Use the graph.

Complete the sentence about the graph. Use a word from the list.

elastic linear non-linear plastic

The graph of current against potential difference for the resistor is........

This diagram shows a cell connected in series with a resistor.

Calculate the potential difference of the cell in the diagram.

Use the equation: potential difference = current × resistance

A student uses the circuit shown in the diagram to measure the resistance of a resistor. M1 and M2 are meters.

Explain the purpose of the variable resistor in the diagram.

Explain why meter M1 in the diagram must be an ammeter.

When meter M1 in the diagram is replaced by a voltmeter, no current flows.

Suggest why.

The graph shows the student’s results from using the circuit.

Calculate the resistance of the resistor. Use the graph.

Complete the sentence about the graph to explain the relationship between potential difference and resistance.

Use words from the list.

decreases increases stays the same

As the potential difference increases, the resistance........

Which voltmeter shows a reading of 0.5 V?

Draw lines to connect each circuit component with its correct symbol.

Circuit component
Symbol

The potential difference across a 3 resistor is 4.5 V.

Calculate the current in the resistor.

Use the Equation Sheet.

A teacher connects the circuit in Fig. 11.2. Fig. 11.2

Both lamps are lit. The teacher then removes lamp A from its holder but leaves the rest of the circuit unchanged.

Describe what happens. Give a reason for your answer.

The teacher connects the circuit in Fig. 11.3. Fig. 11.3

Both lamps are lit. The teacher then removes lamp A.

Describe what happens. Give a reason for your answer.

The graph shows how the current in a resistor changes when the potential difference across the resistor changes.

Which two statements about the graph are correct?

Tick (✓) two boxes.

A teacher builds the circuit shown in the diagram.

Give the total resistance of the circuit.

The voltmeter reads 4 V.

Calculate the ammeter reading. Use the Data Sheet.

Calculate the potential difference across the cell.

15* (a) A student investigates if resistance changes as current changes.

The student can use this equipment:

Describe the method the student should follow to work out if the resistance of the 10 cm wire changes as current changes and describe how to use the results to calculate resistance.

You can include a diagram in your answer.

The student writes a risk assessment for the investigation.

Suggest a possible hazard for this investigation.

How can the student reduce the risk from the hazard?

A student does an experiment to measure the resistance of a coil of wire.

The diagrams in Fig. 15.1 show the meters used in this experiment:

Meter V measures potential difference.

Complete the table to describe meter V.

Name of meter V

Smallest change in potential difference that can be measured on meter V

Draw a circuit diagram for the experiment.

Use the symbol for a fixed resistor to represent the coil of wire that the student is testing.

Write down the values of potential difference and current shown by the meters in Fig. 15.1.

Calculate the resistance of the coil of wire.

Resistance =........

To improve the experiment, the student places the coil of wire in a beaker of water, as shown in Fig. 15.2.

Suggest two reasons why this improves the experiment.

The student adds a variable resistor in series with the wire.

Suggest two reasons why this improves the method.

A student wants to check the electrical power of a mains filament lamp.

He sets up the circuit in Fig. 11.1.

Complete the table to describe how he sets up the equipment in Fig. 11.1.

The student reads the meters in the circuit in Fig. 11.1.

• The value of the potential difference is 230 V.

• The value on the ammeter is 0.5 A.

Calculate the actual power of the mains filament lamp.

Use the equation: power = potential difference × current

Another lamp has a power of 100 W. 1 kW = 1000 W

What is the power of the lamp in kilowatts (kW)?

0.1 kW 1 kW 100 kW 100 000 kW

Suggest how the student can make his readings more precise.

Fig. 11.2 shows a night-light. It contains a 1.0 W lamp and a 3.0 V battery.

The student compares the mains filament lamp with the night-light. They are both used for the same amount of time.

Fig. 11.2

Use these words to complete the sentences.

You can use each word once, more than once, or not at all.

more than less than equal to

The energy transferred by the night-light is …………………………… the energy transferred by the mains filament lamp.

The power of the night-light is …………………………… the power of the mains filament lamp.

A student makes a ‘component tester’. He connects a diode to a small filament lamp.

This is a diagram of the component tester.

Describe how the student could use the component tester to find the positive (+) terminal of a cell.

Here is a graph of current against potential difference for a diode.

The diode is not a fixed resistor.

Describe two ways the graph shows this.

Calculate the resistance of the diode at + 0.8 V.

Use the graph and the equation: potential difference = current resistance

Resistance =........

The manufacturer of the diode gives the following warning:

The supply voltage must not exceed 1 V.

Use the graph in 16(b) to explain why.

Sketch a graph of current against potential difference for a filament lamp. Use the axes below.

A student makes a ‘component tester’. He connects a diode to a small filament lamp.

This is a diagram of the component tester.

Describe how the student could use the component tester to find the positive (+) terminal of a cell.

Here is a graph of current against potential difference for a diode.

The diode is not a fixed resistor.

Describe two ways the graph shows this.

Calculate the resistance of the diode at + 0.8 V.

Use the graph and the equation: potential difference = current × resistance

The manufacturer of the diode gives the following warning:

The supply voltage must not exceed 1 V.

Use the graph in 11(b) to explain why.

Sketch a graph of current against potential difference for a filament lamp. Use the axes below.

A student has one cell and two lamps. She wishes to connect them so that both lamps have maximum brightness.

Draw a complete circuit diagram to show how she can achieve this.

The student then investigates an unknown component. She records values for current through the component and the potential difference across the component.

Plot a graph of the data and draw a line of best fit.

One of the points has already been completed for you.

Describe what these results show.

Calculate the resistance of the unknown component.

Use the equation: Resistance = Potential difference ÷ Current

A student uses a small motor to lift a toy car through a vertical distance of 1.0 m.

The car has a weight of 0.05 N.

Calculate the work done when lifting the car through this distance.

Calculate the power of the motor if the car takes 5.0 seconds to travel the 1.0 m distance.

State the unit.

The motor uses 2 cells in series.

Each cell has a potential difference of 1.5 V.

Write down the total potential difference of the cells.

The motor has a resistance of 6.0 .

Calculate the current in the circuit when the motor is in use.

Use the equation: Potential difference = Current × Resistance

The student wishes to increase the time taken to lift this toy car vertically through the 1.0 m distance shown.

Suggest a change he could make to this experiment to achieve this.

A student uses a small motor to lift a toy car through a vertical distance of 1.0 m.

The car has a weight of 0.05 N.

Calculate the work done when lifting the car through this distance.

Calculate the power of the motor if the car takes 5.0 seconds to travel the 1.0 m distance.

State the unit.

The motor uses 2 cells in series.

Each cell has a potential difference of 1.5 V.

Write down the total potential difference of the cells.

The motor has a resistance of 6.0 .

Calculate the current in the circuit when the motor is in use.

Use the equation: Potential difference = Current × Resistance

The student wishes to increase the time taken to lift this toy car vertically through the 1.0 m distance shown.

Suggest a change he could make to this experiment to achieve this.