Series & Parallel Circuits (AQA GCSE Physics: Combined Science)

The circuit in Figure 1 shows how an LDR can be used to turn on a circuit when it gets dark.

Figure 1

If the light intensity decreases, what happens to the current and the potential difference across the LDR?

When the potential difference across the LDR is 3 V, what is its resistance?

Explain your answer.

When the light gets dimmer, the resistance of the LDR becomes 1000 .

Calculate the current through the LDR when its resistance is 1000.

Give your answer to 3 significant figures.

A student has four resistors.

Each resistor has a resistance of 100.

The four resistors are connected in series with a 3 V cell, as shown in Figure 2 below.

Figure 2

Calculate the current that flows through the cell.

Give your answer to 3 significant figures.

A student set up the circuit in Figure 3 below.

Figure 3

Calculate the potential difference across the 80  resistor.

Switch X is closed.

State what will happen to the total resistance of the circuit and the current through the circuit.

The circuit diagram in Figure 8 shows two resistors connected in parallel.

Figure 8

Reading on ammeter A₁ = 3 A

Reading on ammeter A₂ = 1 A

Using the circuit diagram in Figure 8, answer the questions below:

The resistance of the variable resistor R₂ is increased.

What would happen to:

• The current through R₂
• The potential difference across R₂
• The current through the battery?

Tick () three boxes

Figure 4 below shows how two resistors can be connected in series or in parallel to a 12 V cell.

The resistors are identical.

Figure 4

Figure 5 shows how an ammeter can be used to measure the current flowing through the battery for the same circuit.

Figure 5

The reading on the ammeter is 1.6 A.

The resistors are identical.

State the current through resistor R₂.

Figure 6 shows a fixed resistor connected in series with a variable resistor.

Figure 6

The resistance of the variable resistor can be varied between 100Ω  and 800Ω .

When the variable resistor is set to 100 Ω, voltmeter 1 reads 12 V and voltmeter 2 reads 3 V.

A student investigated how the total resistance of a circuit varied with resistors placed in parallel.

Figure 1 shows the circuit the student used.

Figure 1

The resistance of each resistor is identical.

The student used an ohmmeter to measure the total resistance.

The student took multiple readings and calculated a mean.

Table 1 shows their results.

Table 1

Determine the missing value X for Reading 3.

Reading 4 = 15.2 Ω

The student's partner said that Reading 4 should not be included in the mean.

State whether you agree, and explain your answer.

Figure 2

Use the graph in Figure 2 to identify the relationship between the mean total resistance and the number of resistors in parallel.

A homeowner is completing renovations on their property.

They install a security light that switches on automatically when it gets dark.

Figure 1 shows the circuit for the security light.

What happens to the resistance of the LDR, and what happens to the current in the circuit when it gets dark?

Tick (✓) one box.

Resistance increases, current increases
Resistance increases, current decreases
Resistance decreases, current increases
Resistance decreases, current decreases

The homeowner also installs a hob in the kitchen. Figure 2 shows the circuit for the hob.

Figure 2

Explain the benefits of connecting the heating elements in parallel.

Table 1 shows the maximum current that can flow safely through copper wires with varying cross-sectional areas.

Table 1

Household power sockets are fitted with copper cables with a cross-sectional area of 2.5 mm².

Explain why it would not be safe to plug the hob into a standard power socket.

Figure 1 shows a circuit constructed by a student.

Figure 1

Determine the readings on ammeters A₂ and A₃.

Figure 2 shows another circuit the student built.

Figure 2

Determine the reading on the ammeter and voltmeter.

Figure 3 shows another circuit constructed by the student.

Figure 3

Determine the resistance of resistor Z.

A homeowner employs an electrician to install a new shower.

The homeowner chooses to use an electrician rather than doing it himself because if he touches the live wire he will receive an electric shock.

Explain why touching the live wire would cause an electric shock.

Some electrical appliances are fitted with an earth wire.

Describe how an earth wire acts as a safety feature