Electric Current and Ohm's law Test

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Electric Current and Ohm's law Test - 6

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Question 1
1 / -0.25

Conversion of temperature into electric voltage is done with

A
thermometer

B
resistor

C
thermistor

D
rheostat

Solution

To convert temperature to voltage we can do a precise measurement of the temperature in a room. A NTC resistor or a thermistor
It is used as a sensor that has a strong temperature dependence.
Question 2
1 / -0.25

For semiconductors, the major factor affecting the value of resistivity when temperature changes is

A
n: the number of free electrons per unit volume

B
e: the charge of an electron

C
m: the mass of an electron

D
τ:average time between collisions

Solution

n increases with temperature and this increase more than compensates any decrease in relaxation time. Hence, for semiconductors resistivity decreases with the increase in temperature.
Question 3
1 / -0.25

When a conductor is placed in an external electric field, the acceleration of its electrons will be

A

B

C

D

Solution

F=-eE .
we know that,
F= ma ,
then
a=F/m.
a=-eE/m.
Question 4
1 / -0.25

Resistors can be wire bound or carbon resistors. Wire bound resistors are generally made of

A
Aluminium

B
Carbon

C
Copper

D
Manganin

Solution

A Nichrome or manganin is commonly used as the metal wires in wire-wound resistors because they provide high resistance to the electric current and operate at high temperature.
Question 5
1 / -0.25

The dimension of the temperature coefficient of resistivity is

A
(temperature.ohm)^-1

B
same as temperature.ohm

C
same as (temperature)^-1

D
same as (temperature)²

Solution

The resistance of a material at temperature T is given by
R=R₀ [1+α(T −T₀ )]
Where R₀ = resistance at reference temperature T ₀ =0^o C and αis the temperature coefficient of resistance.
From the above equation, the unit of the temperature coefficient is per degree Celsius (/^o C). So, dimension will be [C⁻¹ ]
Question 6
1 / -0.25

The winding of a motor has a resistance of 80 ohms at 15 °C. Find its resistance at 50 °C. the temperature co-efficient of resistance is 0.004/°C

A
60.57 Ω

B
75.47 Ω

C
90.56 Ω

D
80.0 Ω

Solution
Question 7
1 / -0.25

On heating a conductor its resistance

A
depends on type of metal

B
remains constant

C
increases

D
decreases

Solution

Heating a conductor makes it more difficult for electricity to flow through it. These collisions cause resistance and generate heat.Heating the conductor causes atoms to vibrate more, which in turn makes it more difficult for the electrons to flow, increasing resistance.
Question 8
1 / -0.25

Specific resistance of a conductor increases with

A
Increase in cross-section and decrease in length

B
Increase in cross-section

C
Decrease in cross-section

D
Increase in temperature

Solution

Resistance of a conductor is given by R = ρl/A,
where ρis the specific resistance, l is the length and A is the cross-sectional area of the conductor.
Now, when l = 1 and A = 1, R = ρ. So specific resistance or resistivity of a material may be defined as the resistance of a specimen of the material having unit length and unit cross-section. Hence, specific resistance is a property of a material and it will increase with the increase of temperature, but will not vary with the dimensions (length, cross section) of the conductor.
Question 9
1 / -0.25

A steady current flows in a metallic conductor of non-uniform cross-section. The quantity/quantities constant along the length of the conductor is/are

A
Current and drift speed

B
Current, electric field and drift velocity

C
Speed only

D
Current only.

Solution

Current does not depend on the area of the conductor; hence it remains a constant.
Current density is inversely a constant.
Current density is inversely proportional to area (i.e.,) J ∝1/A electric field drift speed is also inversely proportional to area (i.e.,) E ∝1/A ,V_d ∝1/A
Hence current is constant along the conductor.
Question 10
1 / -0.25

A current of 2 ampere is passing through a metallic wire of cross-sectional area 2 x 10^-6 m² . If the density of the charge carriers in the wire is 5 x 10²⁶ m^-3 , then the drift velocity of the electrons will be

A
1.15 x 10^-6 m/s

B
1.5 x 10^-5 m/s

C
1.25 x 10^-2 m/s

D
1.05 x 10^-3 m/s

Solution

Drift velocity, v=I/nAe
=2/(2x10^-6 )x(5x10²⁶ )x(1.6x10^-19 )
=1.25x10^-2 m/s

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Electric Current and Ohm's law Test - 6

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Electric Current and Ohm's law Test - 6

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Question 1

thermometer

resistor

thermistor

rheostat

Solution

Question 2

n: the number of free electrons per unit volume

e: the charge of an electron

m: the mass of an electron

τ:average time between collisions

Solution

Question 3

Solution

Question 4

Aluminium

Carbon

Copper

Manganin

Solution

Question 5

(temperature.ohm)-1

same as temperature.ohm

same as (temperature)-1

same as (temperature)2

Solution

Question 6

60.57 Ω

75.47 Ω

90.56 Ω

80.0 Ω

Solution

Question 7

depends on type of metal

remains constant

increases

decreases

Solution

Question 8

Increase in cross-section and decrease in length

Increase in cross-section

Decrease in cross-section

Increase in temperature

Solution

Question 9

Current and drift speed

Current, electric field and drift velocity

Speed only

Current only.

Solution

Question 10

1.15 x 10-6 m/s

1.5 x 10-5 m/s

1.25 x 10-2 m/s

1.05 x 10-3 m/s

Solution

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(temperature.ohm)^-1

same as (temperature)^-1

same as (temperature)²

1.15 x 10^-6 m/s

1.5 x 10^-5 m/s

1.25 x 10^-2 m/s

1.05 x 10^-3 m/s