Series and parallel circuits

Figure 1 shows two lamps in series in a circuit.

The resistance of each lamp is 12 Ω.

Calculate the total resistance of the lamps in the circuit.

total resistance of lamps =_........

The current in a lamp in Figure 1 is 0.50 A.

The resistance of the lamp is 12 Ω.

Calculate the voltage across this lamp.

Use the equation

V = I × R

The voltage across a different lamp is 4.5 V.

The current in this lamp is 0.40 A.

Calculate the energy transferred to the lamp in 5 minutes.

Use the equation

E = I × V × t

energy transferred =_........

Figure 2 shows a circuit with a switch, two ammeters and two resistors in series with a cell.

Which of these statements is true for the circuit in Figure 2?

The resistance of the circuit is increased by adding one resistor to the circuit.

State how increasing the resistance changes the current in the circuit.

A student connects a resistor across the terminals of a 9 V battery.

There is a current of 6 mA in the resistor.

Calculate the resistance of the resistor.

Describe how an additional component could be used to vary the current in the resistor.

A voltmeter has four different scales.

Which one of these scales would be most suitable to measure a voltage of 0.85 V?

*(c) The table in Figure 23 gives some information about series and parallel circuits.

Describe how a student can use ammeters and voltmeters to investigate the information given in Figure 23.

Your answer should include

• circuit diagrams showing how the currents and voltages can be measured

• a comparison of the results that would be expected

Space for circuit diagrams

Answer lines for this question are on page 37.

Figure 20 is a circuit diagram.

The current at P is

Some students investigate resistors in parallel.

The students set up a circuit containing four identical resistors.

The circuit used is shown in Figure 21.

Figure 21

The students measure the current from the power supply and the voltage (p.d.) across the resistors.

On Figure 21, draw a voltmeter connected to measure the voltage (p.d.) across the resistors.

T he students remove one resistor and measure the current and voltage again with only 3 resistors in the circuit.

T hey repeat the measurements of current and voltage with only 2 resistors in the circuit and then with only 1 resistor in the circuit.

Figure 22 is a table of their results.

Using data from the table in Figure 22, predict the current from the power supply when there are 4 resistors in the circuit.

current =_........

Using data from the table in Figure 22, calculate the resistance of only 1 resistor.

resistance =_........

Using data from the table in Figure 22, explain what happens to the total resistance of the circuit as the number of resistors in parallel decreases.

An electric fire is connected to a 230 V mains supply.

A current of 9.0 A is supplied to the fire.

Calculate the power supplied to the fire.

Use the equation

power = current voltage

power =_........

Figure 4 is a circuit diagram.

The current at P is

Some students investigate resistors in parallel.

The students set up a circuit containing four identical resistors.

The circuit used is shown in Figure 5.

Figure 5

The students measure the current from the power supply and the voltage (p.d.) across the resistors.

On Figure 5, draw a voltmeter connected to measure the voltage (p.d.) across the resistors.

T he students remove one resistor and measure the current and voltage again with only 3 resistors in the circuit.

T hey repeat the measurements of current and voltage with only 2 resistors in the circuit and then with only 1 resistor in the circuit.

Figure 6 is a table of their results.

Using data from the table in Figure 6, predict the current from the power supply when there are 4 resistors in the circuit.

current =_........

Using data from the table in Figure 6, calculate the resistance of only 1 resistor.

resistance =_........

Using data from the table in Figure 6, explain what happens to the total resistance of the circuit as the number of resistors in parallel decreases.

Figure 3 shows the parts in an electrical circuit.

Draw the circuit diagram of this electrical circuit in the space provided.

The battery symbol and some of the connecting wires have been drawn for you.

Figure 4 shows the current flowing into and out of point P in part of a circuit.

Which of these is the value of current I ?

There is a current of 0.46 A in a lamp.

Calculate the total charge that flows through the lamp in 30 seconds.

Use the equation

charge = currenttime in seconds

The voltage across the lamp is 6.0 V.

The current in the lamp is 0.46 A.

Calculate the energy transferred to the lamp in one minute.

Use the equation

energy transferred = currentvoltagetime in seconds

energy transferred =_........

Figure 19 shows a lamp connected to a d.c. power supply.

The power supply provides a potential difference (voltage) of 4.5 V.

The current in the lamp is 0.30 A.

Calculate the resistance of the lamp.

Use the equation

Calculate the power supplied to the lamp.

Another identical lamp is added to the circuit, as shown in Figure 20.

The power supply provides the same potential difference as it provided in the circuit in Figure 19.

State and explain the difference between the brightness of the lamp in Figure 19 and the brightness of a lamp in Figure 20.

A student is given a low voltage power supply and 1 m of resistance wire.

The student uses these and other pieces of equipment to measure the resistance of just 50 cm of the resistance wire.

Draw a diagram of the circuit that the student should use.

Your circuit diagram should identify the pieces of equipment that the student uses.

Describe the difference between direct current (d.c.) and alternating current (a.c.) in electrical circuits.

Figure 3 shows a lamp connected to a d.c. power supply.

The power supply provides a potential difference (voltage) of 4.5 V.

The current in the lamp is 0.30 A.

Calculate the resistance of the lamp.

Use the equation

Calculate the power supplied to the lamp.

Another identical lamp is added to the circuit, as shown in Figure 4.

The power supply provides the same potential difference as it provided in the circuit in Figure 3.

State and explain the difference between the brightness of the lamp in Figure 3 and the brightness of a lamp in Figure 4.

A student is given a low voltage power supply and 1 m of resistance wire.

The student uses these and other pieces of equipment to measure the resistance of just 50 cm of the resistance wire.

Draw a diagram of the circuit that the student should use.

Your circuit diagram should identify the pieces of equipment that the student uses.

A technician investigates different electrical devices that are used in a car.

The technician connects a device to the 12 V car battery.

The technician measures the current in the circuit and the potential difference (voltage) across the device.

Figure 17 shows the car battery and the device that is being tested.

Draw on Figure 17 to show how the circuit should be completed so that the current in the circuit and voltage across the device can be measured.

The technician tests a headlamp.

The current in the headlamp is 4.8 A when connected to the 12 V battery.

Calculate the power supplied to the headlamp.

The technician tests an interior light.

The current in the interior light is 600 mA when connected to the 12 V battery.

Calculate the energy transferred to the interior light in 7 minutes.

Use an equation selected from the list of equations at the end of the paper.

The technician connects four devices to the car battery.

Each device is connected to its own switch and its own fuse.

Figure 18 shows how the four devices, fuses and switches are connected.

The current in each device is shown next to the device.

Calculate the current in the wires to the battery when all the devices are switched on.

State how the overall resistance of the circuit changes when any one of the devices is switched off.

There is a current of 2.3 A in the radio when the radio is working correctly.

Which of these should the technician choose to protect the radio circuit?

Explain why the wires to the battery in a car are thicker than the wires that connect each device to its switch and its fuse.

A student investigates resistors connected in series in an electrical circuit.

The student has

The student does not know the value of the resistor marked X.

The student decides to measure the potential difference (voltage) across resistor X.

Figure 15 shows the circuit that the student connected.

The circuit is connected incorrectly.

Describe how the student should correct the mistake.

The student corrects the mistake.

The voltage across resistor X is 2.1 V.

The circuit is connected to a 3 V battery.

State the value of the voltage across the 22 Ω resistor.

The current in resistor X is 0.041 A.

The voltage across resistor X is 2.1 V.

Show that the resistance of resistor X must be about 50 ohms.

Use the equation

Calculate the power in resistor X when the voltage across X is 2.1 V and the current in resistor X is 0.041 A.

Calculate the overall resistance of the 22 ohm resistor and resistor X.

The current in the circuit is 0.041 A.

The voltage across the battery is 3.0 V.

Calculate the energy transferred in 2 minutes.

Use the equation

A student investigates resistors connected in parallel using a number of resistors. Each resistor has the same resistance.

Figure 19 shows a circuit diagram with one resistor, R.

Add to Figure 19:

a voltmeter to find the potential difference across resistor R

another resistor in parallel with resistor R.

State the measurements that the student must take to find the overall resistance of the resistors in parallel.

The student investigates how the overall resistance of the circuit changes when additional resistors are added in parallel to R.

Each resistor has the same resistance.

Figure 20 shows the results of the student’s investigation.

State the resistance of a single resistor.

Comment on the relationship between the overall resistance of the circuit and the number of resistors in parallel.

Use information from Figure 20 to support your answer.

A different circuit is then set up with two resistors as shown in Figure 21.

Calculate the potential difference across the 15 Ω resistor.

Calculate the total power dissipated when there is a current of 0.20 A in the two resistors.

Use the equation

power produced_........

Figure 1 gives the names of three atomic particles and some descriptions of the charge on the particles and their position in the atom.

Draw one straight line from each atomic particle to its correct description.

Figure 2 shows the junction of three wires, F, G and H, in a circuit. The current in wire F is 6.0 A. The current in wire G is 3.5 A.

Calculate the current in wire H.

A wire in a circuit carries a current of 0.9 A. Calculate the quantity of charge that flows through the wire in 50 s.

State the unit of charge with your answer.

Use the equation

charge = current × time

A resistor is connected to a power supply.

The potential difference across the resistor is 6.0 V.

Which of these corresponds to a potential difference of 6.0 V?

The resistor remains connected for a period of time.

The current in the resistor is 200 mA.

A total charge of 42 C flows through the resistor.

Calculate, in minutes, the time taken for this amount of charge to flow through the resistor.

Calculate the total energy transferred by the 6.0 V power supply when a charge of 42 C flows through the resistor.

The resistor becomes warm while there is a current in it.

Explain why the resistor becomes warm.

Figure 16 shows a cardboard tube with a wire coming out from each end.

There are two 10 ohm resistors inside the cardboard tube.

A potential difference of 6.0 V is connected between P and Q.

There is a current of 1.2 A in the wires.

Deduce how the resistors have been arranged inside the cardboard tube.

Figure 18 shows identical filament lamps connected together to a 12 V power supply.

Calculate the potential difference across each lamp.

The power output of each lamp is 0.75 W

Calculate the resistance of each lamp.

*(b) Explain, with the aid of a circuit diagram, the method a student could use to investigate how the resistance of a single lamp changes with the potential difference across the lamp.

Equations