Paper 1 Semiconductors and Diodes Drills

Q1

A semiconductor has conductivity

A. between conductor and insulator.
B. always infinite.
C. always zero.
D. identical to copper.

Q2

Heating an intrinsic semiconductor generally

A. decreases mobile carrier number.
B. increases mobile carrier number.
C. removes all holes.
D. makes resistance infinite always.

Q3

An NTC thermistor has resistance that

A. increases with temperature.
B. decreases with temperature.
C. is independent of temperature.
D. is zero at all temperatures.

Q4

An LDR has resistance that decreases when

A. light intensity increases.
B. temperature decreases only.
C. voltage is zero only.
D. magnetic field increases.

Q5

A diode conducts much more easily when

A. forward biased.
B. reverse biased.
C. unconnected.
D. cooled to absolute zero.

Q6

The I-V characteristic of a diode is

A. linear and symmetric.
B. non-linear and asymmetric.
C. always horizontal.
D. identical to ohmic resistor.

Q7

In reverse bias, ideal diode current is approximately

A. zero.
B. maximum.
C. negative infinite.
D. equal to supply current always.

Q8

Rectification converts an alternating input into

A. a unidirectional pulsating output.
B. a larger ac only.
C. zero voltage.
D. a magnetic field only.

Q9

Half-wave rectification uses

A. one half-cycle mainly.
B. both half-cycles in opposite directions through load.
C. no diode.
D. capacitor only.

Q10

A potential divider output depends on

A. where output is measured.
B. sensor resistance trend only.
C. supply colour.
D. wire length only.

Q11

If output is across the lower resistor, $V_{out}=$

A. $V_s{R}_{lower}/(R_{upper}+R_{lower})$.
B. $V_s{R}_{upper}/(R_{upper}+R_{lower})$.
C. $V_s/R_{lower}$.
D. $R_{lower}/V_s$.

Q12

For an NTC thermistor as lower resistor, increasing temperature makes $V_{out}$

A. decrease.
B. increase always.
C. unchanged always.
D. negative.

Q13

For an LDR, bright light usually makes resistance

A. smaller.
B. larger.
C. infinite.
D. negative.

Q14

A diode is not ohmic because

A. its resistance is not constant.
B. it has no current ever.
C. it obeys $V=IR$ with constant $R$.
D. it is always metallic.

Q15

A typical forward-biased silicon diode at room temperature and moderate current has a forward p.d. of about

A. $0.6$ to $0.7\mathrm{V}$.
B. $230\mathrm{V}$ always.
C. $0\mathrm{V}$ exactly.
D. $100\mathrm{V}$.

Q16

A smoothing capacitor in a rectifier circuit is connected

A. across the load.
B. only in series with the diode always.
C. in place of the source.
D. to ground only.

Q17

The output of a rectifier without smoothing is

A. steady like an ideal battery.
B. pulsating.
C. always sinusoidal with negative halves.
D. zero.

Q18

In a diode circuit, forward bias means the anode is at

A. higher potential than cathode.
B. lower potential than cathode.
C. same potential only.
D. negative infinity.

Q19

Sensor circuits often use semiconductors because their resistance changes with

A. physical conditions such as temperature or light.
B. mass only.
C. gravity only.
D. wavelength of sound only.

Q20

A diode is connected in series with a resistor to a d.c. supply. Reversing the diode while leaving the supply unchanged will usually

A. greatly reduce the current.
B. leave the current exactly unchanged.
C. make the resistor’s resistance negative.
D. double the supply voltage.