TRANSISTORSPast Paper Questions and Answers

2013 2EP01– Q11(b)The circuit below is a monostable timing circuit, When activated component C turns on for a fixed time period.

Name the components labelled A, B and C. [3]

A electrolytic capacitor (1) B 555 Timer (1) C bulb (1)

2013 2EP01– Q11(c)The circuit below is a monostable timing circuit, When activated component C turns on for a fixed time period.

because the 555 Timer cannot supply the current (1) the bulb needs to light (1)

(c) Explain why a transistor has been used between components B and C. [2]

2012 2EP01– Q14(a)(iv)The illustration below is part of a logic circuit.

connect a transistor (1) to the circuit output (1)

(a)(iv)The output current from component B is too low.

Describe one way in which this current could be increased.

[2]

2011 2EP01– Q1Which one of the following components is an input device? [1]

(1)

2011 2EP01 – Q11(b)A student is making a nightlight. This is a circuit which will automatically switch a lamp on when it becomes dark. The circuit is shown below.

(b) Name the components labelled A, B and C. [3]

A LDR (1) B LED (1) C transistor (1)

2011 2EP01 – Q11(c)A student is making a nightlight. This is a circuit which will automatically switch a lamp on when it becomes dark. The circuit is shown opposite.

(c) Component D is a variable resistor.

Describe the purpose of component D in the circuit. [2]

it allows the light level at which the circuit switches (1) to be easily adjusted (1)

2011 2EP01 – Q11(d)A student is making a nightlight. This is a circuit which will automatically switch a lamp on when it becomes dark. The circuit is shown opposite.

(d) Use the formula R = V/I to calculate the resistance of R1 when 7 volts across it gives a current of 2mA. Remember to include the units in your answer.

[3]

current I = 0.002A (1) substitute into formula: R = 7V / 0.002A answer: 3500 (1) Ω (1) (or 3k5 (1) Ω (1))

2011 2EP01 – Q14(d)(iii)(d) The circuit opposite is a time delay circuit. When the switch is moved to the position shown, the LED will

come on after a short time delay.

(iii) Discuss the function of R1, C1 and the transistor in creating the time delay. [3]

C1 charges up (1) through R1(1) and the transistor switches on when its base

voltage reaches 0.6V (1)

2010 2EP01– Q1Which one of the following components is a sensor?

[1]

(1)

2010 2EP01 – Q11(b)(i)(b) A student is making a game using the circuit below.

(i) Name the components labelled A, B and C. [3]

A variable resistor (1) B electrolytic capacitor (1) C transistor (1)

2010 2EP01 – Q11(b)(ii)(b) A student is making a game using the circuit below.

(ii) Describe the function of component C in this circuit. [3]

it switches on the LED (1) when its base voltage reaches 0.6V (1)

SAM 2EP01– Q1Which of the following components is an output device?[1]

(1)

SAM 2EP01 – Q11(b)(i)(b) A student is making a desk fan using the circuit shown below.

(i) Name the components labelled A, B and C. [3]

A SPST switch (1) B thermistor (1) C motor (1)

2009 1974 FT – Q2(a)(i)The diagram below shows a transistor switching circuit.

(a)(i) Name the components D1, C1, VR1 and R3. [4]

D1 LED (1) C1 capacitor (1) VR1 variable resistor (1) R3 LDR (1)

2009 1974 FT – Q2(a)(ii)The diagram below shows a transistor switching circuit.

(a)(ii) State the action of D1 in the circuit when the transistor (TR1) switches on. [1]

D1 lights up (1)

2009 1974 FT – Q2(a)(iii)The diagram below shows a transistor switching circuit.

(a)(iii) Give the reason for using R2 in the circuit. [1]

it protects the transistor (1)

2009 1974 FT – Q2(a)(iv)The diagram below shows a transistor switching circuit.

(a)(iv) Give one reason for using VR1 in the circuit. [1]

it allows the light level at which the circuit switches to be easily changed (1)

2009 1974 FT – Q2(a)(v)The diagram below shows a transistor switching circuit.

(a)(v) Give one reason why SW1 is in the circuit. [1]

to switch the circuit on and off (1)

2008 1974 HT – Q2(a)(iii)A warning signal sounds when the guard of a machine is left open. The warning signal is generated by a combination of two Astables and a logic gate.

A simplified block diagram of the warning signal system is shown below.

(iii) Name one appropriate transducer driver for the warning signal system. [1]

transistor (1)

2007 2EP01 – Q11(a)

(a) The table below shows some tools and components.

Complete the table below by giving the missing names and uses. [1]

transistor (1) electronic switch (1)

2007 1974 HT – Q2(b)(i)A designed bicycle alarm contains a combination of logic gates and a timer circuit to make it work. Shown below is a simplified block diagram of the bicycle alarm system.

(i) Explain the reason why a buzzer connected to an integrated circuit will not work. [2]

the IC can only supply a low current (1) which is not enough for the buzzer to work (1)

(b) When the output of the AND gate was connected to the buzzer the circuit did not work.

2007 1974 HT – Q2(b)(ii)A designed bicycle alarm contains a combination of logic gates and a timer circuit to make it work. Shown below is a simplified block diagram of the bicycle alarm system.

(ii) Describe one way in which a named interface device may be used to drive the buzzer. [2]

connect a transistor (1) between the AND gate and the buzzer (1)

(b) When the output of the AND gate was connected to the buzzer the circuit did not work.

2007 1974 FT – Q2(a)The diagram below shows a simple locker alarm.

(a) Name the components A, B, C and E. [4]

A battery (1) B SPST switch (1) C LDR (1) E buzzer (1)

2007 1974 FT – Q2(b)The diagram below shows a simple locker alarm.

(b) Give one reason for using R3 in the circuit. [1]

it protects the transistor (1)

2007 1974 FT – Q2(c)The diagram below shows a simple locker alarm.

(c) Give one reason for using VR1 in the circuit. [1]

it allows the light level at which the circuit switches to be easily changed (1)

2007 1974 FT – Q2(e)The diagram below shows a simple locker alarm.

(e) Describe the action of the circuit when the base of the transistor passes the

switch-on voltage. [2] the transistor switches on (1) and the buzzer

sounds (1)

2007 1974 FT – Q2(f)The diagram below shows a simple locker alarm.

(f) Explain one reason for using the diode (D1) in the circuit. [2]

protects the transistor (1) from the back emf generated by the buzzer (1)

2006 1974 HT – Q2(c)(i)A 555 Astable is used to generate the pulses for a loudspeaker circuit.

(c) When the alarm circuit is activated it needs a short time

delay before the loudspeaker sounds. This allows the user time

to re-set it. The circuit opposite gives this time delay.

(i) Use the axis below to show how the voltage at point A rises when switch SW1 is closed. [2]

• protects the transistor (1) from the back emf generated by the buzzer (1)

2006 1974 HT – Q2(c)(ii)A 555 Astable is used to generate the pulses for a loudspeaker circuit.

(c) When the alarm circuit is activated it needs a short time

delay before the loudspeaker sounds. This allows the user time

to re-set it. The circuit opposite gives this time delay.

(ii) The transistor (TR1) acts as an electronic switch. Give the typical base voltage when

TR1 is fully switched on. [1]

0.6V (1)

2004 1974 HT – Q4(a)(i)A child’s toy used red and green LEDs.

(a) The output part of a control circuit for the toy is shown opposite

(i) Give one reason why D1 is used in the circuit. [1]

it protects the transistor (1)

2004 1974 HT – Q4(a)(ii)A child’s toy uses red and green LEDs.

(a) The output part of a control circuit for the toy is shown opposite

(ii) Describe the actions of D2 and D3 when the transistor (TR1) is switched on. [2]

D2 will light (1)

D3 will switch off (1)

2004 1974 FT – Q2(a)(i)

(a) Part of the circuit design to

control a burglar alarm is shown

opposite.

(i) Name the components marked X, Y and Z. [3]

X battery (1) Y transistor (1) Z LDR (1)

2004 1974 FT – Q2(a)(ii)

(a) Part of the circuit design to

control a burglar alarm is shown

opposite.

(ii) Component T is a light emitting diode (LED).

Describe one working property of an LED. [2]

the LED will only light up (1) if its anode is more positive than the cathode (1)

2004 1974 FT – Q2(a)(iii)

(a) Part of the circuit design to

control a burglar alarm is shown

opposite.

(iii) State one purpose of component R1 in the circuit. [1]

it protects the LED (1)

2004 1974 FT – Q2(a)(iv)

(a) Part of the circuit design to

control a burglar alarm is shown

opposite.

(iv) Explain one purpose of component VR1 in the circuit. [2]

it allows the light level at which the circuit switches (1) to be easily adjusted (1)

2003 1974 HT – Q2(b)(i)The output from a logic gate becomes an input to the circuit shown below.

(b)(i) Describe the action of the transistor (TR1), when the input to the circuit is binary 1. [2]

it switches on (1) because the base voltage is greater than 0.6V (1)

2003 1974 HT – Q2(b)(ii)The output from a logic gate becomes an input to the circuit shown below.

(b)(ii) Describe the action of the LED when the transistor is switched on.

[2] it switches on (1) because the cathode of the LED is more negative than its anode. (1)

2003 1974 HT – Q2(b)(iii)A motor and diode are connected in parallel with the LED and resistor R2, as shown below.

(b)(iii) Explain why TR1 is needed in this circuit, rather than connecting the motor directly to the logic gate. [2]

because the logic gate cannot supply the high current (1) the motor need to work (1)

2003 1974 FT – Q2(a)(i)Part of a circuit design to control a greenhouse heater is shown below.

(a)(i) Name the components X, Y and Z. [3]

X diode (1) Y relay (1) Z transistor (1)

2003 1974 FT – Q2(a)(ii)Part of a circuit design to control a greenhouse heater is shown below.

(a)(ii) Component T is a thermistor. Describe the working properties of a thermistor. [2]

as the temperature rises (1) the resistance of the thermistor decreases (1)

2003 1974 FT – Q2(a)(iii)Part of a circuit design to control a greenhouse heater is shown below.

(a)(iii) State the purpose of component R1 in the circuit. [2]

protects the transistor (1)

2003 1974 FT – Q2(a)(iv)Part of a circuit design to control a greenhouse heater is shown below.

(a)(iv) Explain the purpose of component VR1 in the circuit. [2]

VR1 sets the temperature (1) at which the circuit switches (1)