KFUPM-Physics102-032

Dr.Aljalal

Sec07

Sec08

Sec09

Recitation ch 27

Answers at the end

Question 1

A cylindrical wire of radius R = 2.0 mm has a uniform current

density J = 2.0*10**(5) A/m**2. What is the current through

the portion of the wire between radial distances R/3 and R/2?

(see figure 1)

a 1.95 A.

b 3.73 A.

c 5.31 A.

d 0.35 A.

e 9.11 A.

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Question 2

A heater element of resistance 10**3 Ohm is constructed

to operate at 110 V. How much thermal energy is produced

in one hour by the heater?

a 4.4*10**4 J.

b 2.2*10**7 J.

c 5.1*10**2 J.

d 6.2*10**5 J.

e 1.9*10**5 J.

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Question 3

A current of 0.300 A is passed through a lamp for 2.00 minutes

using a 6.00-V battery. The energy dissipated by the lamp during

the 2.00 minutes is:

a 216 J

b 20.0 J

c 36.0 J

d 1.80 J

e 12.0 J

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Question 4

A copper wire of cross sectional area 3.00*10**(-6) m**2

and length 4.00 m has a current of 2.25 A uniformly

distributed across that area.

How much electric energy is converted to thermal energy

in 10.0 minutes ?

[The resistivity of copper is 1.68*10**(-8) ohm*m]

a 0.50 J

b 68.0 J

c 13.6 J

d 21.7 J

e 30.2 J

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Question 5

If 4.7*10**(16) electrons pass a particular point in a wire

every minute, what is the current in the wire?

a 2.9*10**(-5) A.

b 1.3*10**(-4) A.

c 4.7*10**(-3) A.

d 2.9*10**(-3) A.

e 9.1*10**(-3) A.

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Question 6

An electric device, which heats water by immersing a

resistance wire in the water, generates 153 J of heat per

second when an electric potential difference of 12 V is

placed across its ends. What is the resistance of the

heater wire?

a 0.81 Ohms

b 0.58 Ohms

c 0.94 Ohms

d 2.10 Ohms

e 0.48 Ohms

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Question 7

At T = 20 degrees-C, the length of a wire is 10 m, and its

cross sectional area is 0.50 mm**2. A potential difference

of 1.0 V is maintained across the ends of the wire. The

resistance of the wire changes by 0.30 ohms for a temperature

change of 50 Celsius degrees.

what is the temperature coefficient of resistivity of the wire ?

At T = 20 degrees, the resistivity is 5.0*10**(-6) ohm*m.

a 15*10**(-3) degrees**(-1)

b 15*10**(-4) degrees**(-1)

c 15*10**(-5) degrees**(-1)

d 6.0*10**(-5) degrees**(-1)

e 6.0*10**(-4) degrees**(-1)

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Question 8

Conduction electrons move to the right in a certain

wire. This indicates that:

a the current density points to the right but

the electric field points to the left.

b the current density and the electric field both

point to the right.

c the current density points to the left but

the electric field points to the right.

d the current density points to the left but

the direction of the electric field is unknown.

e the current density and the electric field both

point to the left.

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Question 9

A metal wire of resistance R is cut into three equal

pieces that are then connected side by side to form a

new wire the length of which is equal to one-third the

original length. What is the resistance of the new wire ?

a R

b R/3

c 9*R

d R/9

e 3*R

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Question 10

A copper wire of cylindrical shape has resistance R.

What is the resistance of a second wire, made of the

same material, that is twice as long and has twice the

diameter ?

a R

b 4R

c 2R

d R/2

e R/4

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Question 11

A copper wire "1" has a length L1 and diameter d1. Another

copper wire "2" has a length L2 and diameter d2. At constant

temperature, the second conductor has smaller resistance if:

a d2 = d1 and L2 > L1.

b d2 < d1 and L2 < L1.

c d2 < d1 and L2 = L1.

d d2 > d1 and L2 > L1.

e d2 > d1 and L2 < L1.

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Answers

1 d

2 a

3 a

4 b

5 b

6 c

7 d

8 e

9 d

10 d

11 e