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Transcript
SCI 3101
Test III
MULTIPLE CHOICE. (3 points each)
1) When two lamps are connected in parallel to a battery, the electrical resistance that the battery senses is
A) more than the resistance of either lamp.
B) less than the resistance of either lamp.
C) none of these
2)
In an electric circuit, the safety fuse is connected to the circuit in
A) parallel.
B) series.
3)
What is the power rating of a light bulb when 0.8 A flow through it when connected to a 120-V outlet?
A) 60 W
B) 120 W
C) 96 W
D) 12 W
E) 15 W
4)
An electric heater is rated at 300 W when used in a 110-V circuit. The safety fuse in the circuit can handle
15 A of current. How many heaters can be safely operated in the circuit?
A) 4
B) 2
C) 3
D) 5
E) more than 5
5)
Like kinds of magnetic poles repel while unlike kinds of magnetic poles
A) attract.
B) may attract or repel.
C) repel also.
6)
Magnetic field lines about a current-carrying wire
A) extend radially from the wire.
C) both of these D) neither of these
7)
An electric motor and electric generator are
A) very similar devices.
B) circle the wire in closed loops.
B) entirely different devices.
8)
When there is a change in the magnetic field in a closed loop of wire,
A) current is made to flow in the loop of wire.
B) electromagnetic induction occurs.
C) a voltage is induced in the wire.
D) all of these
E) none of these
9)
Voltage can be induced in a wire by
A) moving a magnet near the wire.
C) changing the current in a nearby wire.
E) none of these
B) moving the wire near a magnet.
D) all of these
10) A device that transforms electrical energy to mechanical energy is a
A) generator. B) magnet.
C) motor.
D) transformer.
11) Transformers use AC so there will be the required
A) voltage for transformation.
C) change in input current.
E) transfer of energy from coil to coil.
E) none of these
B) change in magnetic field for operation.
D) magnetic field intensities.
12) Metal detectors, like the ones used at airports, are activated by
A) electric fields.
B) alternating current.
C) magnetic fields.
D) electromagnetic induction.
13) A certain transformer doubles input voltage. If the primary coil has 10 A of current, then the current in
the secondary coil is
A) 5 A.
B) 25 A.
C) 2 A.
D) 10 A.
E) none of these
14) The vibrations of a transverse wave move in a direction
A) at right angles to the direction of wave travel.
B) along the direction of wave travel.
15) If the frequency of a certain wave is 10 Hz, its period is
A) 100 s.
B) 10 s.
C) 0.1 s.
D) none of these
16) A standing wave occurs when
A) the amplitude of a wave exceeds its wavelength.
C) two waves overlap.
17) The Doppler effect is characteristic of
A) sound waves.
B) water waves.
B) the speed of the wave is zero or near zero.
D) a wave reflects upon itself.
C) light waves.
D) all of these
18) A bow wave is produced when a wave source moves
A) as fast as the waves it produces.
B) faster than the waves it produces.
C) nearly as fast as the waves it produces.
19) A sound wave is a
A) transverse wave.
B) standing wave.
C) shock wave.
20) The phenomenon of beats results from sound
A) reflection.
B) refraction.
C) interference.
D) longitudinal wave.
D) all of these
21) On some days, air nearest the ground is colder than air that is higher up. On one of these days, sound
waves
A) tend to be refracted upward.
B) travel without refraction. C) tend to be refracted downward.
22) Electromagnetic waves consist of
A) vibrating electric and magnetic fields.
B) compressions and rarefactions of electromagnetic pulses.
C) particles of light energy.
D) high-frequency gravitational waves.
23) The color of an opaque object is the same as the light that is
A) absorbed.
B) transmitted.
C) reflected.
D) none of these
24) The complementary color of blue is
A) cyan.
B) red.
D) green.
25) Magenta light is really a mixture of
A) red and cyan light.
B) yellow and green light.
C) red and yellow light.
D) red and blue light.
C) magenta.
E) yellow.
Problems (5 points each)
1) How much current is consumed by a 1200W hair dryer when connected to a 120V receptacle?
P =V • I
1200W = 120V • I
I = 10 amp
2) What is the total resistance of a circuit which has 3 resistors (R1 = 10 ohms, R2 = 25 ohms, R3 = 140 ohms)
connected in parallel in a circuit containing a 12 volt battery?
1
1
1
1
= +
+
RT R1 R2 R3
=
1
1
1
+
+
10 ohm 25 ohm 140 ohm
= 0.147 / ohm
= 6.80 ohm
3) A ideal transformer has 50 turns in its primary and 250 turns in its secondary, 12 volts AC is connected to
the primary. What is the output voltage?
Input Voltage
Output Voltage
=
# of primary turns # of secondary turns
x
12V
=
50 250
x = 60 V
4) Middle C on a keyboard has a frequency of 256 hertz. If the speed of sound is 340 m/s, what is the
wavelength of this note?
c =ν • λ
340m / s = (256 / s ) • λ
350m / s
λ=
256 / s
=1.33 meters
5) Complete the following color “equations”
White – Cyan = ____RED____________
Blue + Yellow = _____WHITE__________
Red + Green = ______YELLOW___________
Magenta – Blue = ____RED___________