Current, resistance and potential difference

A student builds this electric circuit to measure the temperature of a room.

At 20 °C, the voltage across the thermistor is 3.9 V.

Explain why the reading on the voltmeter is 2.1 V.

The resistor in the circuit has a resistance of 290 Ω.

Calculate the current in the resistor.

Use the formula

voltage = current × resistance

State the reading on the ammeter.

Calculate the resistance of the thermistor.

The student observes that the voltmeter reading increases as the temperature of the room increases.

Explain this observation.

The student wants to use the circuit as a temperature‑measuring device.

They have this additional equipment

• a large beaker

• water at different temperatures

• a thermometer

Describe what measurements the student needs to take so that the circuit could be used as a temperature‑measuring device.

Assume that the thermistor in the circuit is waterproof.

You may draw a diagram to help your answer.

This question is about electrical circuits.

The table shows the circuit symbols for some electrical components.

Complete the table by placing ticks (✓) to show whether each component can visibly indicate the presence of a current in a circuit.

Diagram 1 shows an electrical circuit containing a cell and component X.

The graph shows how the resistance of component X varies with temperature.

Give the name of component X.

Using the graph, determine the resistance of component X when its temperature is 50 °C.

The cell in diagram 1 has a voltage of 9.0 V.

Calculate the current in component X when its temperature is 50 °C.

Use the formula

voltage = current × resistance

The circuit in diagram 1 is modified by adding a second identical component X in series with the other components.

The temperatures of the first component X and second component X are reduced to 26 °C.

Explain how the resistance of the circuit is affected by these changes.

Fluorescent tube lamps can be used in schools and office buildings for lighting.

The photograph shows an engineer installing a fluorescent tube lamp.

Diagram 1 shows a simplified view of the components of a fluorescent tube lamp.

When the lamp is on, a large voltage is applied between the positive electrode and the negative electrode.

State what is meant by the term voltage.

The large voltage causes electrons to accelerate from the negative electrode towards the positive electrode.

An electron gains 1.0 × 10^–16J of energy when it accelerates between the electrodes.

Show that the voltage between the electrodes is about 600 V.

[magnitude of electron charge = 1.6 × 10^–19C]

The electron gains 1.0 × 10^–16J of energy in its kinetic store when it accelerates from the negative electrode to the positive electrode.

Calculate the speed of an electron when it reaches the positive electrode.

Assume the electron is initially at rest.

[electron mass = 9.1 × 10^–31kg]

When the electrons accelerate between the electrodes, they collide with mercury atoms.

Energy is transferred to the mercury atoms during the collisions. This causes the mercury atoms to emit ultraviolet light.

Atoms in the fluorescent coating absorb this ultraviolet light, which is then re‑emitted as light from a different part of the electromagnetic spectrum.

Diagram 2 shows this process.

Suggest why the tube must have a fluorescent coating for the lamp to operate effectively.

Explain why the fluorescent tube lamp is dangerous if the fluorescent coating becomes damaged.

A student investigates different electrical components.

The student first investigates how the voltage of a diode affects the current in the diode.

They use this equipment.

• diode

• cell

• variable resistor

• wires

• voltmeter

• ammeter

Draw a circuit diagram to represent a circuit the student could use.

The diode has been drawn for you.

In the second investigation, the student uses a circuit with two different resistors, A and B, and a battery with a voltage of 2.9 V.

Diagram 1 shows the circuit, and the current in each resistor.

Calculate the current in the battery.

State the formula linking voltage, current and resistance.

Calculate the resistance of resistor A.

Diagram 2 shows the same three components connected in a different circuit.

Resistor B has a resistance of 13 ohms.

Comment on the difference between the current in the battery in Diagram 2 and the current in the battery in Diagram 1.

Use calculations to support your answer.

The diagram shows a domestic lighting circuit.

Explain an advantage of using this circuit for domestic lighting.

When switch 1 is closed, the current in lamp 1 is 22 mA.

Give the name of the charged particle that moves in an electric current.

Show that lamp 1 has a power of about 5 W.

Calculate the energy transferred by lamp 1 when it is on for 30 seconds.

The circuit is connected to the mains supply. Mains voltage is 230 V.

State what is meant by the term voltage.

Switches 1 and 3 are closed, which turn on lamps 1 and 3.

Switch 2 is open.

Calculate the current in the mains supply.

A student investigates the voltage-current characteristics of an unknown component, X.

The student is given this equipment to investigate component X.

• battery

• variable resistor

• ammeter

• voltmeter

• connecting wires

The diagram shows an incomplete circuit containing the battery and component X.

Complete the diagram by drawing a circuit the student could use for their investigation.

The graph shows the results of the investigation.

Draw a line of best fit on the graph.

Calculate the resistance of component X when the voltage is 4.2 V.

Give the unit.

Which of these is equivalent to 4.2 V?

The student concludes that component X is a filament lamp.

Comment on the student’s conclusion.

The photograph shows a power bank used to recharge the battery in an electronic device.

The power bank stores charge.

The charge stored can be measured in amp-hours (Ah). 1 Ah is the amount of charge transferred by a current of 1 A in a time of 1 hour.

Calculate the charge stored in coulombs when the charge stored is 1 Ah.

Use the formula

charge stored = current × time taken

An electronic device is connected to the power bank.

Whilst recharging, the electronic device receives a constant current of 2.4 A and 3.8 × 10³C of charge is transferred.

Calculate the time taken to recharge the electronic device.

Give your answer in minutes.

The electronic device is connected to the power bank using a long cable.

Suggest how using a long cable affects the time taken to recharge the electronic device when compared with a short cable.

A student owns three electronic devices. Each electronic device stores a different amount of charge.

The table gives some information about the charge stored by the electronic devices and how often they need to be recharged.

The power bank stores a maximum charge of 26.8 Ah.

The student needs to take these three electronic devices on a school trip for one week.

Determine whether the maximum charge of the power bank is enough to recharge the batteries of the three electronic devices during the school trip.

This question is about electrical resistors.

Diagram 1 shows a 13 k Ω resistor connected to a 5.8 V battery.

State the formula linking voltage, current and resistance.

Calculate the current in the resistor.

Diagram 2 shows a 200 Ω resistor connected in parallel with a 13 k Ω resistor.

Complete the circuit diagram by adding a suitable meter to diagram 2 to measure the current in the 13 k Ω resistor.

The switch in the circuit is closed.

Explain what happens to the current in the 13 k Ω resistor and the current in the battery.

13 k Ω resistor

battery

A student investigates how the current in a filament lamp changes when the voltage across the lamp is varied.

Draw a circuit diagram the student could use in their investigation.

The graph shows the student’s results.

Describe the relationship between current and voltage shown on the graph.

State the formula linking resistance, voltage and current.

Use the graph to determine the resistance of the filament lamp when the voltage across the lamp is 7.2 V.

A student investigates how the current in a 60 Ω resistor varies with the voltage across the resistor.

The student has access to this equipment

• 12 V battery

• ammeter and voltmeter

• 60 Ω resistor

• variable resistor

• switch

• connecting wires

Draw a circuit diagram to show how the student could connect this equipment to carry out the investigation.

Describe a suitable method the student could use for this investigation.

Complete the current–voltage graph by drawing a line that shows the expected results of the investigation.

The student repeats their investigation with a 120 Ω resistor.

Explain how a current–voltage graph for a 120 Ω resistor compares with the current–voltage graph for the 60 Ω resistor.

Diagram 1 shows a light-emitting diode (LED) and a resistor in series with a cell and an ammeter.

The voltage across the LED is 0.63 V.

Calculate the current in the circuit.

Give your answer in milliamps.

Diagram 2 shows a second LED and an extra resistor connected in parallel with the cell.

The resistor and the LED are the same as the components used in diagram 1. The two resistors are identical and the two LEDs are identical.

Explain how the ammeter reading will change.

Diagram 1 shows a circuit built by a student.

State the formula linking voltage, current and resistance.

Calculate the voltage across the 17 Ω resistor.

State the voltage across the 6.2 Ω resistor.

Calculate the current in the battery.

Diagram 2 shows a second circuit built by the student using the same battery and resistors.

Explain how the current in the battery will change now the resistors are connected in series.

You do not need to do any calculations in your answer.

The diagram shows an electric circuit containing component X and a lamp connected in series.

Add another component to the diagram to measure the voltage of component X.

Give the name of component X.

The graph shows how the resistance of component X changes with light intensity.

Use the graph to determine the resistance of component X when the light intensity is 4.0 arbitrary units.

The current in the circuit is 0.0018 A.

Calculate the voltage across component X at a light intensity of 4.0 arbitrary units.

Explain what happens to the brightness of the lamp when component X is covered with a dark sheet of paper.

A teacher uses this circuit to investigate how the current in a circuit changes with the temperature of a room.

Calculate the voltage across the thermistor.

State the formula linking voltage, current and resistance.

Calculate the resistance of the thermistor.

The graph shows how the resistance of the thermistor changes with temperature.

Describe the relationship between the temperature and the resistance of the thermistor.

Explain how the reading on the voltmeter changes when the temperature of the room decreases.

The diagram shows a circuit that includes a battery, an ammeter, a voltmeter and three different resistors.

Give the voltmeter reading.

State the formula linking voltage, current and resistance.

Calculate the resistance of resistor X.

Give the reason why the reading on the ammeter would be 16 mA.

Calculate the resistance of resistor Y.

Resistor X and the voltmeter are removed from the circuit, leaving a break in this part of the circuit.

Explain how the current in the battery changes when these components are removed.

The photograph shows a mains-operated, decorative lamp, X.

Lamp X has seven identical bulbs that are connected in series.

Give a disadvantage of connecting the bulbs in series.

Suggest an advantage of connecting the bulbs in series.

Each bulb has a working resistance of 390 Ω.

The voltage across each bulb is 33 V.

State the formula linking voltage, current and resistance.

Calculate the current in each bulb.

Calculate the energy transferred to lamp X when it is used for 2.5 hours.

Another decorative lamp, Y, uses five of the same 390 Ω bulbs connected in series.

Both lamps are mains operated.

Explain how the brightness of a single bulb in lamp Y compares to the brightness of a single bulb in lamp X.

The diagram shows some apparatus used to find the mass of an object.

The two pieces of metal foil act as a variable resistor.

When more mass is added, the elastic string stretches and the small piece of metal foil moves to the right.

Draw the circuit diagram for this electrical circuit.

The variable resistor has been drawn for you.

Draw a voltmeter on the diagram to measure the voltage of the variable resistor.

Explain how the voltage across the variable resistor changes if more mass is added to the end of the elastic string.

The student extends the investigation by keeping the mass constant and replacing the cell with a variable power supply.

The student measures the current in the circuit for different voltages.

These are the results.

State the independent variable in the student’s investigation.

Plot the student’s results on the grid.

Draw a line of best fit.

The diagram shows an electric circuit.

When the thermistor is in hot water, its resistance is 490 Ω.

Show that the resistance of the fixed resistor is about 400 Ω.

Explain how the voltage across the fixed resistor changes when the hot water is replaced with cold water.

The diagram shows part of a circuit used for an outdoor lighting system.

Draw a voltmeter on the diagram to measure the voltage of the 4500 resistor.

Give the name of component X.

The voltage across component X is 3.0 V.

Calculate the voltage across the 4500 resistor.

Calculate the current in the circuit.

[voltage = current × resistance]

Calculate the resistance of component X.

Give your answer in k.

resistance =_........ k

Explain where a lamp should be connected in this circuit, so that the voltage across it increases as the light received by component X decreases.

This question is about electric circuits.

Which quantity is defined as the rate of flow of charge?

Which quantity is defined as the energy transferred per unit charge passed?

Diagram 1 shows an electric circuit with two resistors, R and S.

Some of the values of the current are also shown.

Diagram 1

On Diagram 1, draw a voltmeter to measure the voltage of resistor S.

Deduce the readings on the ammeters.

Resistor R has a resistance of 11 Ω.

Calculate the voltage across resistor R.

Explain how the voltage across resistor R compares with the voltage across the battery.

Diagram 2 shows a different circuit containing a battery, an ammeter and a thermistor.

Explain how the thermistor can be used to vary the current in this circuit.

A student is given a type of putty that conducts electricity.

He rolls the putty into cylinders of different cross-sectional area.

The photograph shows the cylinders.

The student investigates how the electrical resistance of the putty is affected by its cross-sectional area.

The diagram shows the cross-sectional area of one of the cylinders of putty.

Use the diagram to determine the mean diameter of the cylinder of putty.

Calculate the cross-sectional area of the cylinder of putty in cm².

[area of a circle = π × radius²]

The student connects a cylinder of putty to a battery.

He measures the voltage of the cylinder and the current in the circuit.

Complete the circuit diagram, adding suitable instruments to measure the voltage of the cylinder and the current in the circuit.

The student uses his voltage and current measurements to calculate the resistance of this cylinder.

He repeats this for other cylinders.

The table shows some of his results.

Calculate the resistance of the cylinder when the cross-sectional area of the cylinder is 24.6 cm².

Give your answer to 3 significant figures.

Plot a graph of resistance on the y-axis and cross-sectional area on the x-axis.

Draw the curve of best fit.

The student extends his investigation by connecting two new identical cylinders to a battery.

The diagram shows the circuit he uses.

He measures the voltage of each cylinder and the total current in the circuit.

Discuss how his measurements of voltage and current compare with the measurements when only one of these cylinders is used.