Series and parallel circuits

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.

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.

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.

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

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.

Diagram 1 shows a simple loudspeaker.

The coil is connected to an alternating current (a.c.) supply.

Describe how the loudspeaker produces sound.

Diagram 2 shows two loudspeakers connected in series with a variable resistor.

The variable resistor is set to 5.0 Ω.

The total voltage across the two loudspeakers is 0.75 V and the current in the circuit is 0.15 A.

Show that the total power of the two loudspeakers is about 0.1 W.

[power = current × voltage]

A student varies the resistance of the variable resistor.

The table shows the power of the loudspeakers for different resistance values of the variable resistor.

Plot the student’s results on the grid.

Draw a curve of best fit.

Diagram 3 shows the loudspeakers connected in series to a cell.

Diagram 4 shows the loudspeakers connected in parallel to the same cell.

Comment on how the total resistance of the loudspeakers in diagram 3 compares with the total resistance of the loudspeakers in diagram 4.

State what is meant by the term electric current.

Diagram 1 shows an electric circuit used to test a fuse.

Give a reason why an LED is included in the circuit.

Add another component to the circuit in diagram 1 to measure the current in the fuse.

Diagram 2 shows a different electric circuit containing three different lamps.

Calculate the current I₁.

State the current I₂.¹

Explain which lamp is the brightest.²

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 containing a cell, two switches and two resistors, R₁ and R₂.

A light emitting diode (LED) is represented using the symbol

Draw a LED on the circuit diagram that will indicate when there is a current in resistor R₁.

Both switches in the circuit are now closed.

Draw an ammeter on the circuit diagram that will measure the current in the cell.

The voltage across the cell is 4.5 V.

Explain how the voltage across R₂ compares with the voltage across the cell.

Switch 1 is now opened whilst switch 2 remains closed.

State the formula linking energy transferred, charge and voltage.

The voltage across the cell stays constant at 4.5 V.

Calculate the charge transferred through the cell when the cell transfers 4.1 J of energy.

A student investigates how the current in resistor R₂ varies with the voltage across it.

Describe how the circuit could be modified for the student to do this investigation.

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.

A toaster is an electrical device used for toasting bread.

The toaster contains thin metal wires.

These wires get hot when there is a current in them.

The wires transfer energy to the bread by heating and by radiation.

Give a reason why the wires in the toaster are connected in parallel.

State the formula linking power, current and voltage.

The power rating of the toaster is 2.8 kW.

Calculate the total current in the toaster.

[mains voltage = 230 V]

The toaster contains 48 thin metal wires.

Calculate the current in each of the thin metal wires.

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 a demonstration to show the link between current and charge.

The diagram shows two metal plates, X and Y, with a metal ball moving between them.

The two metal plates have no charge before the power supply is connected.

When plate Y is connected to the positive terminal of the power supply, the plate becomes positively charged.

Explain how plate Y gains a positive charge.

The metal ball becomes positively charged when it touches plate Y.

The metal ball then moves away from plate Y towards plate X.

Explain why the metal ball moves away from plate Y.

Give a reason why the ball is made of metal.

When the metal ball moves away from plate Y to plate X, a charge of 5.1 × 10^-6 C is transferred.

State the formula linking charge transferred, current and time taken.

Calculate the current if the metal ball takes 0.45 seconds to travel from plate Y to plate X.

Suggest why the current increases if the voltage of the power supply is increased.

Give the name of the apparatus that can be used to measure current.

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.