Series and parallel circuits

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.

Body analysis scales use the electrical resistance of a person’s legs to estimate the percentage of water in the person’s body.

Figure 8 shows body analysis scales.

The person’s legs contain both solid tissue and water.

A student used resistors to model the solid tissue and water.

The student connected a 20 resistor in parallel with a resistor, R.

Figure 9 shows the circuit diagram.

To determine the total resistance of both resistors, a voltmeter must be connected into the circuit.

Complete Figure 9 to show where the voltmeter should be connected.

The student calculated the total resistance of the two resistors.

The student’s answer was 26 .

Explain why the student’s answer cannot be correct.

Use the Physics Equations Sheet to answer questions 06.3 and 06.4.

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

When the total resistance of the resistors was 7.5 the current in the circuit was 480 mA.

Calculate the potential difference across the two resistors.

The student investigated how the resistance of R affected the total resistance of

the circuit.

Table 2 shows the results.

Some of the results are plotted in Figure 10.

Figure 10

Complete Figure 10.

You should:

• label both axes

• plot the two remaining values from Table 2

• draw the line of best fit.

What resistance of R would give a total resistance of 4.4 ?

Use Figure 10.

The body analysis scales initially show a reading of 0.0 kg.

When the student steps onto the scales the reading is 64.8 kg.

The student steps off the scales and then immediately steps back on.

The scales now show a reading of 64.1 kg.

Complete the sentence.

The difference between the two values given by the scales is due

to a
error.

The height of the student is programmed into the scales.

The scales place the student into a category, A, B or C, based on height and mass.

Figure 11 shows how the scales use the category and the total resistance of the legs to determine the body water percentage.

The total resistance of the student’s legs is 600 k. A healthy body water percentage is between 45% and 65%.

The different measurements of the mass of the student mean that the student could be in either category A or category B.

Evaluate if the student has a healthy body water percentage.

Body analysis scales use the electrical resistance of a person’s legs to estimate the percentage of water in the person’s body. Figure 3 shows body analysis scales.

The person’s legs contain both solid tissue and water. A student used resistors to model the solid tissue and water. The student connected a 20 resistor in parallel with a resistor, R. Figure 4 shows the circuit diagram.

To determine the total resistance of both resistors, a voltmeter must be connected into the circuit. Complete Figure 4 to show where the voltmeter should be connected.

The student calculated the total resistance of the two resistors. The student’s answer was 26 . Explain why the student’s answer cannot be correct.

Use the Physics Equations Sheet to answer questions 02.3 and 02.4.

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

When the total resistance of the resistors was 7.5 the current in the circuit was 480 mA. Calculate the potential difference across the two resistors.

The student investigated how the resistance of R affected the total resistance of

the circuit. Table 1 shows the results.

Some of the results are plotted in Figure 5.

Figure 5

Complete Figure 5. You should:

• label both axes

• plot the two remaining values from Table 1

• draw the line of best fit.

What resistance of R would give a total resistance of 4.4 ? Use Figure 5.

The body analysis scales initially show a reading of 0.0 kg.

When the student steps onto the scales the reading is 64.8 kg. The student steps off the scales and then immediately steps back on. The scales now show a reading of 64.1 kg.

Complete the sentence. The difference between the two values given by the scales is due

The height of the student is programmed into the scales. The scales place the student into a category, A, B or C, based on height and mass. Figure 6 shows how the scales use the category and the total resistance of the legs to determine the body water percentage.

The total resistance of the student’s legs is 600 k. A healthy body water percentage is between 45% and 65%. The different measurements of the mass of the student mean that the student could be in either category A or category B. Evaluate if the student has a healthy body water percentage.

Figure 7 shows how the National Grid transfers energy from a power station to some street lamps.

Explain how transformer X increases the efficiency of the National Grid.

The potential difference across the primary coil in transformer Y is 400 000 V. The potential difference across the secondary coil is 11 000 V. The current in the primary coil is 660 A. Calculate the current in the secondary coil of transformer Y. Use the Physics Equations Sheet.

Why is the current in each street lamp less than the current in the secondary coil in transformer Y ? Tick (✓) one box.

Figure 8 shows the top of a street lamp.

The light sensor detects if it is day or night. Figure 9 shows part of the circuit in the light sensor.

Explain what happens to the potential difference across resistor R as the light intensity decreases.

When the current in resistor R is 20 mA, the power transferred by resistor R is 6.0 W. Calculate the resistance of resistor R. Use the Physics Equations Sheet.

A TENS machine uses an electrical current to relieve pain. Figure 8 shows the electrodes of a TENS machine connected across an ankle.

The maximum power of the TENS machine is 240 mW. The potential difference across the battery in the TENS machine is 2.5 V. Calculate the maximum current from the battery.

Figure 9 is a sketch graph showing how the potential difference across the electrodes varies with time.

A student concluded that there was an alternating potential difference across the electrodes. How does Figure 9 show that the student was not correct?

Figure 10 shows a circuit the student built using the battery from the TENS machine.

The student recorded how the current in the resistor varied with the potential difference across the resistor. Figure 11 shows a sketch graph of the results.

What relationship does Figure 11 show?

Figure 12 shows two more circuits that the student built using the battery from the TENS machine.

The resistors all have the same resistance. Compare the readings on the voltmeter and ammeter in circuit A and circuit B.

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

Figure 2 shows a circuit that a student built.

The lamp has a resistance of 10 Ω Each resistor has a resistance of 10 Ω What is the total resistance of the circuit?

Tick (✓) one box.

Explain your answer to Question 04.1

The student replaced one of the resistors with a thermistor.

Draw the circuit symbol for a thermistor in the box below.

The student increased the temperature of the thermistor. Explain how the current in the thermistor changed.

Figure 3 shows another circuit the student built.

Explain how the potential difference across the resistor and the lamp will change when the switch is closed.

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.