Current Electricity Test

Result

Current Electricity Test - 6

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Weekly Quiz Competition

Question 1
4 / -1

The resistance of a heating element is 99Ω at room temperature. What is the temperature of the element if the resistance is found to be 116Ω? (Temperature coefficient of the material of the resistor is 1.7 × 10^−4∘C⁻¹)

A
999.9^∘C

B
1005.3^∘C

C
1020.2^∘C

D
1037.1^∘C

Solution

Here, R₀ = 99Ω, T₀ = 27^∘C
R_T = 116Ω;
α = 1.710^−4∘C⁻¹
∴ R_T= R₀[1 + α(T − T₀)]
∴ R_TR₀− 1 = α(T − T₀)
⇒ 11699 − 1= α(T − T₀)

=
∴
⇒ T = 1010.1 + T₀ = 1010.1 + 27
= 1037.1^∘C
Question 2
4 / -1

The resistance of the wire in the platinum resistance thermometer at ice point is 5Ω and at steam point is 5.25Ω. When the thermometer is inserted in an unknown hot bath its resistance is found to be 5.5Ω. The temperature of the hot bath is

A
100^oC

B
200^oC

C
300^oC

D
350^oC

Solution

Here,R₀ = 5Ω, R₁₀₀ = 5.25Ω, R_t= 5.5Ω
As,R₁ = R₀(1 + αt)
∴R₁₀₀ = R₀(1 + α100)

Equation (i) and (ii), we get

= 200^oC
Question 3
4 / -1

The resistance of wire in a heater at room temperature is 65Ω. When the heater is connected to a 220V supply the current settles after a few seconds to 2.8A. What is the steady temperature of the wire. (Temperature coefficient of resistance α = 1.70 × 10^−4∘C⁻¹)

A
955^∘C

B
1055^∘C

C
1155^∘C

D
1258^∘C

Solution

Here, T₁ = 27^∘C, R₁ = 65Ω
R₂
= Supply voltage / Steady current
= 220 / 2.8
= 78.6Ω
Now, using the relation
R₂ = R₁[1 + α(T₂− T₁)]
∴

T₂ − T₁ = 1231
T₂ = 1231 + T₁ = 1231 + 27
= 1258C^∘
Question 4
4 / -1

A wire has a resistance of 2.5Ω at 28^∘C and a resistance of 2.9Ω at 100^∘C. The temperature coefficient of resistivity of material of the wire is

A
1.06 × 10^−3∘C⁻¹

B
3.5 × 10^−2∘C⁻¹

C
2.22 × 10^−3∘C⁻¹

D
3.95 × 10^−2∘C⁻¹

Solution

Here, R₁= 2.5Ω, T₁ = 28^∘C
R₂ = 2.9Ω and T₂= 100^∘C
As R₂ = R₁[1 + α(T₂ − T₁)]
∴ 2.9 = 2.5[1 + α(100 − 28)]

=
= 2.22 × 10^−3∘C⁻¹
Question 5
4 / -1

Figure (a) and figure (b) both are showing the variation of resistivity (p) with temperature (T) for some materials. Identify the types of these materials.

A
Conductor and semiconductor

B
Conductor and Insulator

C
Insulator and semiconductor

D
Both are conductor

Solution

In conductors due to increasein temperature the resistivity increases and in semiconductors if the decreases exponentially.