Physics Written Test Key
PHYSICS WRITTEN TEST KEY
Topic: PN junction, diodesDate : ……….
Name: ______Class 5C
Pass 90 points
Multiple choice activity: you are forbidden to erase and change your written choice
Multiple choice + Filling the blanks activities score : 116/150
4 points for each right choice
0 point for each wrong choice
1 point for each missing choice
Give reasons of the choice if requested, or it is invalid
True / False activity score:4/150
1 point for each right choice
0,5 point for each missing choice
0 point for each wrong choice
Problem score: 30/150, see the enclosed rubric
1.When matching polarity connections have been made and the potential difference (PD) is above 0.7 V, the diode is considered to be:
A. not working
B. forward biased
C. reverse biased
D. an open switch
2.What is the current through the LED?
A. 0 mA
B. 23 mA
C. 18 mA
D. 13 mA
3.Since diodes are destroyed by excessive current, circuits must have:
A. higher voltage sources
B. current limiting resistors
C. more dopants
D. higher current sources
4.Testing a good diode with an ohmmeter should indicate
A. high resistance when forward or reverse biased
B. low resistance when forward or reverse biased
C. high resistance when reverse biased and low resistance when forward biased
D. high resistance when forward biased and low resistance when reverse biased
5.What is the current through the diode?
A.1 mA
B. 0.975 mA
C. 0.942 mA
D. 0.0 mA
6.A pn junction allows current flow when
A. the p-type material is more positive than the n-type material
B. the n-type material is more positive than the p-type material
C. both the n-type and p-type materials have the same potential
D. there is no potential on the n-type or p-type materials
7.When a diode is forward biased, the voltage across it
A. is directly proportional to the current
B. is inversely proportional to the current
C. is directly proportional to the source voltage
D. remains approximately the same
8.With a 12 V supply, a silicon diode, and a 370-ohm resistor in series, what voltage will be dropped across the diode?
A. 0.3 V
B. 0.7 V
C. 0.9 V
D. 1.4 V
9. The area at the junction of p-type and n-type materials that has lost its majority carriers is called the
A. barrier potential
B. depletion region
C. n region
D. p region
10.DC power should be connected to forward bias a diode as follows:
A. – anode, + cathode
B. – cathode, – anode
C. + anode, – cathode
D. + cathode, + anode
11.At any given time in an intrinsic piece of semiconductor material at room temperature
A. electrons drift randomly
B. recombination occurs
C. holes are created
D. All of the above
12.A reverse biased diode will act as an open switch.
A.TrueB.False
13.If the diode in a series circuit is reverse biased, the resistor will drop all the applied voltage.
A.TrueB.False
14.Reverse biasing a pn junction allows the flow of majority current.
A.TrueB.False
15.Doping semiconductive material is the process of putting a small amount of pentavalent or trivalent atoms in with tetravalent atoms.
A.TrueB.False
16. A ___ is created when an electron moves from the valence band to the conduction band.
- holeB.gap C. vacancyD. blank
17.Typically the forward voltage on an LED is between ______and ______.
A. 1.5 V, 3.7 V
B. 0.7 V, 1.1 V
C. 1 V, 3 V
D. 1 V, 6 V
18.The name of the circuit in the given circuit is the___.
A. half-wave rectifier
B. center-tapped full-wave rectifier
C. full-wave bridge rectifier
D. half-wave bridge rectifier
19.The small amount of ac signal present on the output of a filtering network for a dc power supply is known as ______.
A. pulsating dc
B.trickle
C.ripple
D. waffle
20.
Atoms in a silicon crystal are held together by ___ bonds.
A. crystal
B. chemical
C. electrical
D. covalent
21.
The peak output voltage from the circuit in the given circuit equals ___.
A. 3 V
B. 3.7 V
C. 2.3 V
D. 0 V
22.An electron can move to another atom's orbit only while in the ______.
A. valence band
B. conduction band
C. orbit nearest the nucleus
D. covalent band
23.___ occurs when a pn junction is first formed.
A. Recombination
B. Covalent bonding
C. Crystallization
D. Breakdown
24.
Connecting a capacitor filter to the circuit in the given circuit will___.
A. produce a nearly-constant dc voltage
B. reduce the output voltage
C. increase the ripple voltage
D. lower the surge current
25.A pure semiconductor material ___ very well.
A. conducts
B. insulates
C. conducts and insulates
D. neither conducts nor insulates
26.Single-element semiconductors are characterized by atoms with ____ valence electrons.
A. 3
B. 4
C. 5
D. 2
27.Under normal conditions a diode conducts current when it is
A. reverse-biased.
B. forward-biased.
C. avalanched.
D. saturated.
28.A diode conducts when it is forward-biased, and the anode is connected to the ______through a limiting resistor.
A. positive supply
B. negative supply
C. cathode
D. anode
29.An n-type semiconductor material
A. is intrinsic.
B. has trivalent impurity atoms added.
C. has pentavalent impurity atoms added.
D. requires no doping.
30.The boundary between p-type material and n-type material is called
A. a diode.
B. a reverse-biased diode.
C. a pn junction.
D. a forward-biased diode.
31.What types of impurity atoms are added to increase the number of conduction-band electrons in intrinsic silicon?
A. bivalent
B. octavalent
C. pentavalent
D. trivalent
32.Doping of a semiconductor material means
A. that a glue-type substance is added to hold the material together.
B. that impurities are added to increase the resistance of the material.
C. that impurities are added to decrease the resistance of the material.
D. that all impurities are removed to get pure silicon.
33.The forward voltage across a conducting silicon diode is about
A. 0.3 V.
B. 1.7 V.
C. –0.7 V.
D. 0.7 V.
34.Which lamps are alight? Some may not be full brightness. (30 points)
Draw other two circuits, which simulate the behaviour of the circuits aboveat the best, showing only the lighting lamps. Give reasons for the choice you made.
Which are the brightest lamps?
