Current, resistance and potential difference

Figure 2 shows circuit symbols for some electrical components.

A student connects a circuit to measure the current in a filament lamp.

The student uses:

• an ammeter

• a cell

• a filament lamp.

Draw a circuit diagram for a circuit the student could use to measure the current in a filament lamp.

You should use three of the circuit symbols from Figure 2.

Which component is the source of energy for the circuit?

Tick () one box.

There is a current of 1.5 A in the filament lamp for a time of 30 s.

Calculate the charge flow in the filament lamp.

Use the equation:

charge flow = current × time

The current in the filament lamp is 1.5 A when the potential difference across the filament lamp is 12 V.

Calculate the resistance of the filament lamp.

Use the equation:

Choose the unit from the box.

Figure 3 shows how the current varies with potential difference for the filament lamp.

Describe the relationship between potential difference and current for the filament lamp.

As the current in the filament lamp increases, the temperature of the filament lamp increases.

What happens to the resistance of the filament lamp as the temperature increases?

In most homes, filament lamps have been replaced with LED bulbs.

Table 1 shows information about a filament lamp and an LED bulb.

Explain the advantages of using LED bulbs instead of filament lamps.

You should include a calculation in your answer.

A student investigated the resistance of a resistor.

The student used:

• the resistor

• a cell

• a switch

• an ammeter

• a voltmeter.

Draw a circuit diagram for a circuit the student could use to measure the resistance of the resistor.

The student:

• added a variable resistor to the circuit

• used the variable resistor to change the readings on the ammeter and the voltmeter

• recorded several different pairs of readings from the ammeter and the voltmeter.

When the reading on the ammeter was 450 mA, the reading on the voltmeter was 2.7 V.

Calculate the resistance of the resistor.

Use the Physics Equations Sheet.

The student plotted a graph of current against potential difference for the fixed resistor.

Complete Figure 2 to show a sketch graph for a fixed resistor at a constant temperature.

Figure 2

Figure 3 shows five resistors with the same resistance but different power ratings.

The power rating of a resistor is the maximum energy the resistor can transfer each second without overheating.

Each resistor has a resistance of 2.2 kΩ.

Determine which resistors in Figure 3 are suitable to be used in a circuit that has a maximum current of 0.012 A.

Use the Physics Equations Sheet.

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.

Figure 10 shows an electric whisk that plugs into the mains electricity supply.

The whisk can mix food by spinning a beater.

Give two energy stores that increase when the whisk is switched on.

Use the Physics Equations Sheet to answer questions 06.2 and 06.3.

Work is done by the whisk when it is used to mix food.

Write down the equation that links power (P), time (t) and work done (W).

The power output of the whisk is 92 W.

Calculate the time for the whisk to do 23 000 J of work.

Use the Physics Equations Sheet to answer questions 06.4 and 06.5.

Which equation links current (I), power (P) and resistance (R)?

Tick (✓) one box.

The current in the whisk is 500 mA.

The resistance of the whisk is 640 Ω.

Calculate the power of the whisk.

The whisk has several settings that allow the beater to spin at different speeds.

A faster beater speed needs a greater power input from the mains electricity supply.

What is the potential difference between the live wire and neutral wire in the mains electricity supply?

Changing the beater speed does not change the potential difference between the live wire and neutral wire.

The power input to the whisk changes because the current in the whisk changes.

Complete the sentence.

When the beater speed increases, the current in the whisk increases because the

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.

A student investigated how the potential difference across a filament lamp affects the current in the lamp.

Figure 1 shows the circuit the student used.

Figure 2 shows a circuit symbol.

What component does the symbol represent?

Tick (✓) one box.

Which component from Figure 1 did the student use to adjust the potential difference across the lamp?

When the voltmeter was not connected to the circuit it gave a reading of 0.4 volts.

How can the student correct all the readings taken from the voltmeter?

Tick (✓) one box.

The student recorded three values of current for each potential difference.

Table 1 shows the results for 2.5 volts.

Calculate the mean current in the lamp.

Calculate the power of the lamp when the potential difference across the lamp was 4.8 V

The current in the lamp was 0.75 A

Use the equation:

power = potential difference × current

Calculate the resistance of the lamp when the potential difference across the lamp was 4.8 V

The current in the lamp was 0.75 A

Use the equation:

Complete the sentence.

Choose answers from the box.

Each answer may be used once, more than once or not at all.

Increasing the current in a filament lamp makes the temperature

Which graph shows the relationship between potential difference and current for a filament lamp?

Tick (✓) one box.

A filament lamp breaks if the electric current in the filament becomes too big.

What is the correct symbol for a filament lamp?

Tick (✓) one box.

What is meant by an electric current?

Tick (✓) one box.

A manufacturer investigated the maximum current value of some filament lamps.

Figure 6 shows the symbols for an ammeter, a battery and a variable resistor.

The manufacturer connected an ammeter, battery, filament lamp and variable resistor in series.

Draw a circuit diagram to show the manufacturer’s circuit.

Include the symbol for a filament lamp from Question 03.1

How could the manufacturer increase the current in the filament lamp?

Tick (✓) one box.

When the potential difference across a filament lamp was 0.75 V, the current in the filament lamp was 0.16 A.

Calculate the power of the filament lamp.

Use the equation:

power = potential difference × current

Write down the equation which links charge flow (Q), current (I) and time (t).

The manufacturer increased the current in the filament lamp to 200 mA.

Calculate the charge flow through the filament lamp in 15 s.

The manufacturer increased the current in the filament lamp from 200 mA.

The filament in the lamp broke when the current reached 320 mA.

How many times greater than 200 mA was the current at which the filament broke?

The manufacturer tested lots of filament lamps.

The current at which the filament lamps broke was 320 ± 60 mA.

What is the range of currents at which the filament lamps broke?

Tick (✓) one box.

Figure 9 shows a mobile phone with its battery removed.

A student measured the potential difference across the battery and then put the battery into the phone.

What is the equation linking current (I), potential difference (V) and resistance (R)?

Tick (✓) one box.

The current in the electronic circuit in the mobile phone was 0.12 A.

The potential difference across the battery was 3.9 V.

Calculate the resistance of the electronic circuit in the mobile phone.

Write down the equation which links energy (E), power (P) and time (t).

The battery was fully charged when it was put into the mobile phone.

The battery discharged when the mobile phone was switched on.

The average power output of the battery as it discharged was 0.46 watts.

The time taken to fully discharge the battery was 2500 minutes.

Calculate the energy transferred by the battery.

The mobile phone includes a sensor to monitor the temperature of the battery.

Figure 10 shows the circuit symbol for a component used in the sensor.

What component does the circuit symbol shown in Figure 10 represent?

The temperature of the component in Figure 10 increases.

The potential difference across the component remains constant.

Explain what happens to the current in the component.

Figure 1 shows a mobile phone with its battery removed.

A student measured the potential difference across the battery and then put the battery into the phone.

What is the equation linking current (I), potential difference (V) and resistance (R)? Tick (✓) one box.

The current in the electronic circuit in the mobile phone was 0.12 A. The potential difference across the battery was 3.9 V. Calculate the resistance of the electronic circuit in the mobile phone.

Write down the equation which links energy (E), power (P) and time (t).

The battery was fully charged when it was put into the mobile phone. The battery discharged when the mobile phone was switched on. The average power output of the battery as it discharged was 0.46 watts. The time taken to fully discharge the battery was 2500 minutes. Calculate the energy transferred by the battery.

The mobile phone includes a sensor to monitor the temperature of the battery.

Figure 2 shows the circuit symbol for a component used in the sensor.

What component does the circuit symbol shown in Figure 2 represent?

The temperature of the component in Figure 2 increases. The potential difference across the component remains constant. Explain what happens to the current in the component.

A student investigated how the resistance of a wire varies with the length of the wire. Figure 1 shows the circuit used.

The symbols for the voltmeter and ammeter in Figure 1 are not complete. Complete the symbols for the voltmeter and ammeter in Figure 1.

Which variable is the independent variable? Tick (✓) one box.

Which variable is the dependent variable? Tick (✓) one box.

The student took repeat readings of potential difference for a 30 cm length of the wire. The readings were: 0.16 V 0.17 V 0.15 V

Calculate the mean potential difference.

The length of the wire was increased to 60 cm The current in the wire was 0.50 A The mean potential difference across the wire was 0.32 V

Calculate the resistance of the 60 cm length of wire. Use the equation:

Calculate the power dissipated in the 60 cm length of wire. Use the equation: power = potential difference × current

Calculate the charge flow when there is a current of 0.50 A in the wire for 17 s Use the equation: charge flow = current × time

Figure 2 is a sketch graph of the results.

The student repeated the investigation using a thicker wire made from the same metal. For the same length, the thicker wire has a lower resistance. Draw a line on Figure 2 to show how the resistance of the thicker wire varies

A student investigated how the resistance of a piece of wire varies with its length.

Figure 2 shows the circuit used.

Explain why the student needed to adjust the variable resistor each time she changed the length of the wire.

The student recorded three measurements of the potential difference across a 0.10 m length of wire. Table 1 shows the results.

Calculate X in Table 1.

Figure 3 shows the results for five different lengths of the wire.

Describe the relationship between the length of the wire and the resistance of the wire.

A glucometer uses the resistance of a blood sample to calculate the glucose concentration in a person’s blood. A blood sample is put into a small tube, which is put inside the glucometer. The blood then acts like a resistance wire. Figure 4 shows the relationship between the resistance of a blood sample and the glucose concentration.

The glucometer applies a potential difference of 0.90 volts across a blood sample. The glucose concentration of the blood sample is 0.98 grams/litre. Determine the current in the blood sample.

A new tube is used each time a blood sample is tested. Explain why valid results are only obtained if each tube is identical.

A student investigated how the current in a resistor varies with the potential difference across the resistor.

Figure 8 shows part of the circuit used.

The student connected an ammeter and a voltmeter into the circuit.

What is the correct way to connect the ammeter and the voltmeter into the circuit?

The student increased the resistance of the variable resistor.

How did increasing the resistance affect the current in the circuit?

How should the student change the circuit to give negative values for current and potential difference?

Name the type of relationship between current and potential difference for a resistor at constant temperature.

Write the equation which links current, potential difference and resistance.

The current in the resistor was 0.12 A when the potential difference across the resistor was 3.0 V

Calculate the resistance of the resistor.

A student investigated how the current in a resistor varies with the potential difference across the resistor. Figure 1 shows part of the circuit used.

The student connected an ammeter and a voltmeter into the circuit. What is the correct way to connect the ammeter and the voltmeter into the circuit?

The student increased the resistance of the variable resistor. How did increasing the resistance affect the current in the circuit?

How should the student change the circuit to give negative values for current and potential difference?

Name the type of relationship between current and potential difference for a resistor at constant temperature.

Write the equation which links current, potential difference and resistance.

The current in the resistor was 0.12 A when the potential difference across the resistor was 3.0 V Calculate the resistance of the resistor.

Some ceiling lights in the home are connected to the mains by a two-core cable.

Figure 6 shows a ceiling light.

Suggest why some ceiling lights do not have an earth wire.

Write down the equation that links charge flow, current and time.

There is a current of 2.95 A in one of the copper wires for 60 seconds.

Calculate the charge flow through the wire.

Use your equation from question 04.2

Figure 7 shows a current potential difference graph for a piece of copper wire.

Draw another line on Figure 7 for a wire with a different resistance.

Some fuses have a thin piece of copper that melts if the current is too large.

Draw the circuit symbol for a fuse.

Describe how the movement of the copper particles in the wire changes when copper melts.

Old copper wires are melted when they are recycled.

Calculate the energy needed to melt 500 kg of copper at its melting point.

Specific latent heat of fusion of copper = 200 kJ/kg

Use the Physics Equations Sheet.