Electricity Test

Result

Electricity Test - 7

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Weekly Quiz Competition

Question 1
1 / -0

Three unequal resistors in parallel are equivalent to a resistance of 1 ohm. If two of them are in the ratio of 1 : 2 and if no resistance value is fractional (let them be natural numbers), the smallest of the three resistances (in ohms) is
[NTSE - Stage - 1, 2018-19, Andhra Pradesh]

A
6

B
2

C
4

D
3

Solution

If R₂ = 2R₁
By inspection, R₁ = 3 Ω
R₂ = 6 Ω
R₃ = 2 Ω
Question 2
1 / -0

Then r =
[NTSE – Stage – 1, 2018-19, Andhra Pradesh]

A

B

C

D

Solution

Current in PQ = 4 A
Then, r =
Question 3
1 / -0

The identical (in all aspects) metal spheres A, B and C are supported on separate insulated stands and placed in contact as shown in the figure. A charged glass rod rubbed by a silk cloth is kept near the metal sphere A; then charges on A, B and C respectively are:

[NTSE - Stage - 1, 2018-19, Andhra Pradesh]

A
Positive charge, Neutral, Neutral

B
Negative charge, Positive charge, Neutral

C
Negative charge, Neutral, Positive charge

D
Positive charge, Neutral, Negative charge

Solution

When a glass rod is rubbed with silk, it gets positive charge.
On placing the positive charged glass rod near sphere A, due to electrostatic induction, A gets negative charge, B becomes neutral and C gets positive charge.
Question 4
1 / -0

A solid cube of silver has a mass of 84 g. What is the resistance between the opposite faces, given that density of silver is 10.5 g/cm³ and resistivity is 1.6 × 10^-4 Ω cm?
[NTSE - Stage - 1, 2018-19, Chandigarh]

A
0.4 × 10^-4 Ω

B
0.8 × 10^-4 Ω

C
0.4 × 10^-8 Ω

D
0.8 × 10^-8 Ω

Solution

Volume =
∴ L³ =
∴ L = 2 cm
R =
=
= 0.8 × 10^-4 Ω
Question 5
1 / -0

The equivalent resistance of the network of three 2 Ω resistors cannot be
[NTSE - Stage - 1, 2018-19, Chandigarh]

A
0.67 Ω

B
2 Ω

C
3 Ω

D
6 Ω

Solution

2 Ω is not possible by the combination of these three resistances.
Question 6
1 / -0

A bird is in a wire cage hanging from a spring balance. The reading of the balance is taken when the bird is flying about in the cage, and when the bird is at rest in the cage. The first reading will be:
[NTSE - Stage - 1, 2018-19, Chandigarh]

A
Much greater than the second

B
Greater than the second

C
Less than the second

D
Same as the second

Solution

When the bird flies, the normal reaction provided will be zero on the bird. When the bird is not flying, the cage will provide a normal reaction equal to the weight of the bird. So, the first reading will be less than the second.
Question 7
1 / -0

Electric bulb B₁ (1000 W - 250 V) and electric bulb B₂ (100 W - 200 V) are connected across a source of 250 V as shown in figure. What is the potential drop across electric bulb B₂?

[NTSE - Stage - 1, 2018-19, Chandigarh]

A
200 V

B
250 V

C
98 V

D
48 V

Solution
Question 8
1 / -0

Determine the equivalent resistance between points x and y in the following circuit.

[NTSE - Stage - 1, 2018-19, Gujarat]

A

B

C

D

Solution
Question 9
1 / -0

Which formula is not correct for R? (R = Resistance)
[NTSE - Stage - 1, 2018-19, Gujarat]

A

B

C
R = l²t

D

Solution

According to Joule's law of heating, heat produced H = I²Rt, where I is current, R is resistance, and t is time.
Formulae 1, 2 and 4 are correct for resistance.
Question 10
1 / -0

The unit of electric potential difference is
[NTSE - Stage - 1, 2018-19, Gujarat]

A
JC

B

C
J

D

Solution

Electric potential is the amount of work needed to move a unit charge from a reference point to a specific point against an electric field.
Question 11
1 / -0

The current in the circuit shown below is

[NTSE - Stage - 1, 2018-19, Karnataka]

A
1.5 A

B
0.5 A

C
2.5 A

D
0.66 A

Solution

Series connection = 2 + 2 = 4
Question 12
1 / -0

A wire of resistance 12 ohms is bent in the form of a circular ring. The effective resistance between the two points on any diameter of the circle is
[NTSE - Stage - 1, 2018-19, Karnataka]

A

B

C

D

Solution

Two resisters are connected in parallel, so each resistance is 6 ohms.
Question 13
1 / -0

The graph shows V-I characteristics of two resistances, their series combination and parallel combination. Identify the resistances, values and graphs.

[NTSE - Stage - 1, 2018-19, Haryana]

A
Resistance-1 X₁, Resistance-2 X₂, Series X₃, Parallel X₄

B
Resistance-1 X₂, Resistance-2 X₃, Series X₄, Parallel X₁

C
Resistance-1 X₃, Resistance-2 X₂, Series X₁, Parallel X₄

D
Resistance-1 X₄, Resistance-2 X₁, Series X₂, Parallel X₃

Solution

Slope of the I-V graph gives .

So, as
X₁ > X₂ > X₃ > X₄
As we know, R_eq in series combination is most and R_eq in parallel combination will be least.
So, R_eq in parallel = X₄
R_eq in series = X₁
Question 14
1 / -0

In the circuit shown, all the measuring instruments are ideal. The reading in ammeter A₂ will be

[NTSE - Stage – 1, 2018-19, Haryana]

A

B
1 A

C

D
zero

Solution

Resistance of an ideal ammeter is zero. Hence, all the current will pass through ammeter A₁.
Hence, current in A₂ is zero.
Question 15
1 / -0

In a helium gas discharge tube, every second, 40 × 10¹⁸ He⁺ ions move towards the right through a cross-section of the tube, while n electrons move to the left in the same time. If the current in the tube is 8 A towards right, then n = ?
[NTSE - Stage - 1, 2018-19, Maharashtra]

A
10 × 10¹⁸

B
10 × 10¹⁹

C
3 × 10²⁰

D
3 × 10²¹

Solution

Net current = current due to He⁺ + current elements
⇒ 8 Amp =
⇒ = n + 40 × 10¹⁸
But n + 40 × 10¹⁸ = 50 × 10¹⁸
So, n = 10 × 10¹⁸ = 10¹⁹
Question 16
1 / -0

Conductivity of superconductors is:
[NTSE - Stage - 1, 2018-19, Madhya Pradesh]

A
Infinite

B
Very large

C
Very small

D
Zero

Solution

In a superconductor, current can keep flowing "forever" since there is no resistance. So, superconductors have infinite conductivity.
Question 17
1 / -0

The value of 1 kWH in joules is
[NTSE - Stage - 1, 2018-19, Telangana]

A
2.6 × 10⁶ joules

B
1.6 × 10⁶ joules

C
3.6 × 10⁶ joules

D
None

Solution

1 kWH = 10³W × 3600 s
= 3600 × 10³ Ws
= 3.6 × 10⁶ J
Question 18
1 / -0

If the resistance of your body is 1,00,000 Ω, what would be the current that flows in your body when you touch the terminals of a 12 V battery?
[NTSE - Stage - 1, 2018-19, Telangana]

A
10 × 10^-5 A

B
14 × 10^-5 A

C
12 × 10^-5 A

D
None

Solution

V = 12 V
I = = 12 × 10^-5 A