FIELD EFFECT TRANSISTORS

(FETs)Past Paper Questions and Answers

2013 2EP01– Q10Which symbol represents a field effect transistor (FET)? [1]

(1)

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

connect a FET (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]

2010 2EP01– Q2Which one of the following describes a type of switch? [1]

(1)

2010 2EP01– Q9Which one of the following is found on a field effect

transistor (FET)? [1]

(1)

2008 1974 – 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]

FET (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 FET (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.

2005 1974 HT – Q2(e)

(e) The output of the logic circuit does not have enough power to operate the relay. It was

also found that a single transistor was not powerful enough to operate the relay.

Name two devices which are powerful enough to operate the relay. [2]

Darlington Pair (1)FET (1)

A logic circuit is connected to a relay interface, which switches an output circuit as shown opposite.

2004 1974 HT – Q2(b)(i)

(i) Describe one action of the Field Effect Transistor (FET1) when it receives a positive voltage. [2]

the FET switches on (1) because the gate is (2V) more positive than the source (1)

(b) The input signal from a

monostable timer is connected

to the circuit shown opposite.

2004 1974 HT – Q2(b)(ii)

(ii) Explain one reason why FET1 is used as an interface device between the 555

timer and the relay. [2]

(b) The input signal from a

monostable timer is connected

to the circuit shown opposite.

• the timer can only supply a low current (1) which is not enough for the relay to work (1)

2004 1974 HT – Q2(b)(iii)

(iii) A protective resistor is not needed at the gate (G) of FET1.

Give one reason why. [2]

(b) The input signal from a

monostable timer is connected

to the circuit shown opposite.

the FET is a voltage operated device. (1)