Physics Test 273

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Physics Test 273

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Weekly Quiz Competition

Question 1
4 / -1

Two point charges 3 × 10^-6 C and 8 × 10^-6 C repel each other by a force of 6 × 10^-3 N. If each of them is given an additional charge of -6 × 10^-6 C, then the force between them will be

A
2.4 × 10^-3 N (repulsive)

B
2.4 × 10^-3 N (attractive)

C
1.5 × 10^-3 N (repulsive)

D
1.5 × 10^-3 N (attractive)

Solution

Key Idea: Like charges repel each other while unlike charges attract each other.

From Coulomb's law, the force of attraction/repulsion between two point charges q1 and q2 placed a distance r apart is given by
Question 2
4 / -1

Three charges 1 μC, 1μC and 2 μC are respectively kept at the vertices A, B and C of an equilateral triangle ABC of side 10 cm. The resultant force on the charge at C is

A
0.9 N

B
1.8 N

C
2.72 N

D
3.1 N

Solution
Question 3
4 / -1

If the inward flux and outward electric flux from a closed surface respectively are 8 ×10³ units and 4 ×10³ units, then what is the net charge inside the closed surface?

A
-4×10³ coulombs

B
4 ×10³ coulombs

C

D
4 × 10³ε₀

Solution

The charge inside the closed surface is given by

q = net electric flux pass through the surface × ε₀

= (4 × 10³ - 8 × 10³) ε₀

Therefore, q = -4 × 10³ ε₀ coulomb
Question 4
4 / -1

A metallic solid sphere is placed in a uniform electric field as shown. Which path will the lines of force follow?

A
1

B
2

C
3

D
4
Solution
- The electric field is always perpendicular to the surface of a conductor.
- On the surface of a metallic solid sphere, the electric field is perpendicular to the surface and directed towards the centre of the sphere.
Hence, the correct option is (d).
Question 5
4 / -1

An electric dipole placed in a non-uniform electric field experiences

A
A force, but no torque

B
A torque, but no force

C
A force as well as a torque

D
Neither a force nor a torque

Solution

The correct option is (c). In a non-uniform electric field, a dipole experiences a force, which gives it a translational motion, and a torque, which gives it a rotational motion.
Question 6
4 / -1

Directions For Questions

Directions: In the following questions, A statement of Assertion (A) is followed by a statement of Reason (R). Mark the correct choice as.

...view full instructions

Assertion (A): In a cavity in a conductor, the electric field is zero.

Reason (R): Charges in a conductor reside only at its surface.

A
Both A and R are true and R is the correct explanation of A

B
Both A and R are true but R is NOT the correct explanation of A

C
A is true but R is false

D
A is false and R is true

Solution

The charge enclosed by the Gaussian surface surrounding the cavity is zero. Hence, the electric field is also zero. So, the assertion is true. Charges in a conductor reside only at its surface. So, in the cavity there is no charge. So, the reason is also true and properly explains the assertion.
Question 7
4 / -1

Directions For Questions

Directions: These questions consist of two statements, each printed as Assertion and Reason. While answering these questions, you are required to choose any one of the following four responses.

...view full instructions

Assertion : The Coulomb force is the dominating force in the universe.

Reason : The Coulomb force is weaker than the gravitational force.

A
If both Assertion and Reason are correct and the Reason is a correct explanation of the Assertion.

B
If both Assertion and Reason are correct but Reason is not a correct explanation of the Assertion.

C
If the Assertion is correct but Reason is incorrect.

D
If both the Assertion and Reason are incorrect.

Solution

Gravitational force is the dominating force in the universe so assertion is false. Gravitational force is weaker than Coulombic force so, reason is false
Question 8
4 / -1

The potential of the electric field produced by a point charge at any point (x, y, z) is given by V = 3x² + 5, where x, y and z are in metres and V is in volts. The intensity of the electric field at (–2, 1, 0) is

A
+17 V/m

B
–17 V/m

C
+12 V/m

D
–12 V/m

Solution
Question 9
4 / -1

A capacitor of capacitance C₁is charged by connecting it to a battery. The battery is then removed and this capacitor is connected to a second uncharged capacitor of capacitance C₂. If the charge gets distributed equally on the two capacitors, then the ratio of the total energy stored in the capacitors, after connection to the total energy stored in them before connection, is

A
1

B
1/2

C
1/√2

D
1/3

Solution

If Q is the initial charge on capacitor C₁, then the initial energy is given by U_i = Q²/2C₁.

As the two capacitors are connected together and the charge is distributed equally, the charge on each capacitor is Q/2.

Since the potential difference (in a parallel connection) across the two capacitors is also the same, it follows that their capacitance are equal (since C = Q/V).

Thus, C₁ = C₂ = C (say)

Also, Q₁ = Q₂ = Q/2

Therefore, the final energy stored in the two capacitors is
Question 10
4 / -1

Directions For Questions

Directions: In the following question, two statements are given. One is assertion and the other is reason. Examine the statements carefully and mark the correct answer according to the instructions given below.

...view full instructions

Assertion: A parallel plate capacitor is charged by a battery. The battery is then disconnected. If the distance between the plates is increased, then the energy stored in the capacitor will decrease.

Reason: Work has to be done to increase the separation between the plates of a charged capacitor.

A
Both Assertion and Reason are true and Reason is the correct explanation of Assertion.

B
Both Assertion and Reason are true but Reason is not the correct explanation of Assertion.

C
Assertion is true but Reason is false.

D
Assertion is false but Reason is true.

Solution

The charge Q remains unchanged as the battery is disconnected. The capacitance C decreases if the separation between the plates is increased.

Now, energy stored U = Q²/2C

Since Q remains the same and C is decreased, U will increase.

Also, work has to be done to increase the separation between the plates of a charged capacitor.

Hence, option d is correct.

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Re-Attempt Weekly Quiz Competition

Physics Test 273

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Physics Test 273

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Question 1

2.4 × 10-3 N (repulsive)

2.4 × 10-3 N (attractive)

1.5 × 10-3 N (repulsive)

1.5 × 10-3 N (attractive)

Solution

Question 2

0.9 N

1.8 N

2.72 N

3.1 N

Solution

Question 3

-4 × 103 coulombs

4 × 103 coulombs

4 × 103 ε0

Solution

Question 4

1

2

3

4

Solution

Question 5

A force, but no torque

A torque, but no force

A force as well as a torque

Neither a force nor a torque

Solution

Question 6

Both A and R are true and R is the correct explanation of A

Both A and R are true but R is NOT the correct explanation of A

A is true but R is false

A is false and R is true

Solution

Question 7

If both Assertion and Reason are correct and the Reason is a correct explanation of the Assertion.

If both Assertion and Reason are correct but Reason is not a correct explanation of the Assertion.

If the Assertion is correct but Reason is incorrect.

If both the Assertion and Reason are incorrect.

Solution

Question 8

+17 V/m

–17 V/m

+12 V/m

–12 V/m

Solution

Question 9

1

1/2

1/√2

1/3

Solution

Question 10

Both Assertion and Reason are true and Reason is the correct explanation of Assertion.

Both Assertion and Reason are true but Reason is not the correct explanation of Assertion.

Assertion is true but Reason is false.

Assertion is false but Reason is true.

Solution

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2.4 × 10^-3 N (repulsive)

2.4 × 10^-3 N (attractive)

1.5 × 10^-3 N (repulsive)

1.5 × 10^-3 N (attractive)

-4×10³ coulombs

4 ×10³ coulombs

4 × 10³ε₀