Electric Circuits (Cambridge O Level Physics)

Fig. 10.1 shows an arrangement for making an electromagnet.

[1]

The switch is closed. The reading on the ammeter is 1.5 A.

 
Calculate the resistance of the circuit.

A student does an experiment to determine the resistance of a fixed resistor, R.
The student draws an incomplete diagram of the circuit, as shown in Fig. 10.1.

Fig. 10.2 shows a 20 Ω resistor connected to a power supply.

A second 20 Ω resistor is connected in series with the first.

State and explain how this affects the current in the circuit.

A teacher is investigating the resistance of a lamp.

Fig. 10.1 shows part of the circuit she uses. The circuit is incomplete.

[3]

[1]

[2]

Fig. 10.2 represents a different type of circuit.

Fig. 7.1 shows two circuit components.

Fig. 7.1

For each of these components state what causes an increase in its resistance.

thermistor ............................................................

LDR .....................................................................

Fig. 7.2 shows a battery connected to a diode, an ammeter and a resistor. 

Fig. 7.3 shows the current–voltage graph for the diode.

Fig 7.2                                                                                                  Fig 7.3 

The current in the resistor is 2.0 A and the potential difference across the resistor is 5.4 V.
 

[1]

[2]

energy input = ......................................................... [2]

Fig 7.4

Explain what is observed.

[1]

Fig. 9.1 is the current–voltage graph for a filament lamp.

Fig. 9.1

Fig. 9.2 shows an incomplete circuit diagram of the circuit that a student uses to obtain the readings for the graph. 

Fig. 9.2

Complete the circuit diagram using suitable circuit symbols for the lamp, a voltmeter and a variable resistor

The ammeter used by the student has ranges 0−10 A, 0−1 A, 0−100 mA and 0−10 mA.

Describe how the student uses the different ranges to obtain readings which allow all nine points to be plotted precisely on the graph while using the ammeter safely.

State how Fig. 9.1 shows that the lamp does not obey Ohm’s law.

Using Fig. 9.1, determine the resistance of the lamp when:
 

resistance = ...............................................................

[1]

resistance = ...............................................................

[2]

. [2]

[2]

length = ......................................................... [2]

A 4.5 V battery is connected in a circuit with an ammeter, a light-dependent resistor (LDR) and a 1800 Ω fixed resistor. 

Fig. 6.1 is the circuit diagram.

Fig. 6.1

The light incident on the LDR causes its resistance to be 9000 Ω.

Calculate:
 

resistance = ...................................................... Ω [2] 

reading = ....................................................... A [2]

A very bright lamp is switched on and the intensity of the light incident on the LDR increases.
 

 [1]

Fig. 11.1 shows lamps in series. Fig. 11.2 shows lamps in parallel.

The lamps are all identical 6.0 V lamps. In each circuit there are three ammeters A₁, A₂ and A₃.

[1]

Each lamp has a resistance of 12 Ω.

Fig. 8.1 shows a circuit.

The lamp has a resistance of 3.0 Ω. Line XY represents a uniform resistance wire of resistance 6.0 Ω.

Calculate the reading on the ammeter.

Fig. 8.2 shows the circuit with a different connection to the resistance wire and an added resistor. The length XY of the whole resistance wire is 2.0 m. The contact is made at Q where the distance XQ is 0.60 m.

Calculate the resistance of the circuit.

A teacher demonstrates the action of a device. Fig. 10.1 shows the symbol for the device.

State the name of this device.

Fig. 10.2 shows another device being used in a circuit. The circuit contains a 6.0 V lamp.

Fig. 8.1 shows a circuit that contains a battery of electromotive force (e.m.f.) 6.0 V, an ammeter, a 20 Ω resistor and component X.

The p.d. across the 20 Ω resistor is varied from zero to 6.0 V. For each value of p.d. a corresponding current is measured.

On Fig. 8.2, draw a line to indicate how the current measured by the ammeter depends on the p.d. across the 20 Ω resistor.

A second resistor is connected into the circuit in parallel with the 20 Ω resistor.

The circuit shown in Fig. 1 includes three ammeters labelled A₁, A₂ and A₃, and one unknown fixed resistor, R.

The voltmeter connected across R reads 24 V

For the parallel branch determine

Calculate the current through the upper 10 Ω resistor.

Calculate the current in the circuit.

Calculate the value of R.