An electric device, which heats water by immersing a resistance wire in the water, generates 60 cal of heat per second when an electric potential difference of 11 V is placed across its leads. What is the resistance of the heater wire? (Note: 1 cal =

1
An electric device, which heats water by
immersing a resistance wire in the water,
generates 60 cal of heat per second when an
electric potential difference of 11 V is placed
across its leads. What is the resistance of the
heater wire? (Note 1 cal 4.186 J)

1. image
2. image
3. image
4. image
5. image

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2
What maximum power can be generated from an 11-V
emf using any combination of a image - image
resistor and a image - image resistor?

1. 31 W
2. 81 W
3. 53 W
4. 46 W
5. 70 W

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3
How much energy is dissipated as heat during a
two-minute time interval by a image resistor
which has a constant 19-V potential difference
across its leads?

1. 36 J
2. 18 J
3. 65 J
4. 71 J
5. 54 J

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4
If image electrons pass through a image -
image resistor in 12 min, what is the potential
difference across the resistor?

1. 37 V
2. 23 V
3. 34 V
4. 25 V
5. 60 V

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5
A wire (length 2.1 m, diameter 1.2 mm) has a
resistance of image . What is the resistivity
of the material used to make the wire?

1. image
2. image
3. image
4. image
5. image

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6
A rod (length 81 cm) with a rectangular cross
section image has a resistance of image .
What is the resistivity of the material used to
make the rod?

1. image
2. image
3. image
4. image
5. image

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7
If a mile of 24-gauge copper wire has a
resistance of image and the resistivity of
copper is image , what is the radius of the
wire? (1 mile 1.6 km)

1. 0.25 mm
2. 0.62 mm
3. 0.30 mm
4. 0.75 mm
5. 0.18 mm

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8
A small bulb is rated at 6.0 W when operated at
110 V. Find its resistance (in ohms).

1. 0.33
2. 6.0
3. 18
4. 1,800
5. 2,000

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9
The temperature coefficient of resistivity of
iron is image that of carbon is image . An
iron wire and a carbon rod, each having the same
image resistance at image , are then cooled
from that temperature to image . Find the new
ratio of the resistance of the carbon rod to the
resistance of the iron wire at the lower
temperature.

1. -0.10
2. 8.0
3. 3.3
4. -10
5. 10

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10
The electron density in copper is image . The
electron charge is image . When a 1.85 A
current is present in a copper wire with a
image cross-section, find the electron drift
velocity, in m/s, with direction defined relative
to the current density.

1. image
2. image
3. image
4. image
5. image

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11
In the Drude model of electrical conduction, what
quantity is the current density NOT directly
proportional to?

1. the average time interval between successive
   collisions
2. the number of charge carriers per unit volume
3. the square of the electron charge
4. the electric field present in the wire
5. the resistivity of the wire

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12
Light bulb image is rated at 25 W and light
bulb image is rated at 60 W. Both are designed
to operate at 220 V. Which statement is correct?

1. The 25 W bulb has a greater resistance and
   greater current than the 60 W bulb.
2. The 25 W bulb has a greater resistance and
   smaller current than the 60 W bulb.
3. The 25 W bulb has a smaller resistance and
   smaller current than the 60 W bulb.
4. The 25 W bulb has a smaller resistance and
   greater current than the 60 W bulb.
5. We need to know the resistivities of the
   filaments to answer this question.

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13
Electric charge is conserved. As a consequence,
when current arrives at a junction of wires, the
charges can take either of two paths out of the
junction and the numerical sum of the currents in
the two paths equals the current that entered the
junction. Thus, current is _____.

1. a vector
2. a scalar
3. neither a vector nor a scalar

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14
A cylindrical wire has a radius image and
length image If both image and image are
doubled, the resistance of the wire _____.

1. increases
2. decreases
3. remains the same

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15
When does a light bulb carry more current?

1. Just after it is turned on and the glow of the
   metal filament is increasing.
2. After it has been on for a few milliseconds and
   the glow is steady.

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16
Make an order-of-magnitude estimate of the cost
of one person's routine use of a hair dryer for 5
years. If you do not use a blow dryer yourself,
observe or interview someone who does. State the
quantities you estimate and their values.

1. image
2. image
3. image
4. image
5. image

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