The mass of an electron is approximately MCQ with Answer and Explanation

The mass of an electron is approximately
A. 1.67 × 10⁻³¹ kg
B. 1.67 × 10⁻²⁷ kg
C. 9.11 × 10⁻³¹ kg
D. 9.11 × 10⁻²⁷ kg
Answer: Option C
Solution (By JKSSB Mock Tests)
Electron mass 9.11×10⁻³¹ kg, proton ~1.67×10⁻²⁷ kg.

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Question #1
A constant force acting on a body of mass 5 kg changes its speed from 2 m/s to 8 m/s in 10 s. The magnitude of force is
A. 0.5 N
B. 3 N
C. 1 N
D. 5 N

Correct Answer: Option B


Explanation:
Acceleration a = (v-u)/t = (8-2)/10 = 0.6 m/s². Force F = m×a = 5 × 0.6 = 3 N. Alternatively, impulse = change in momentum = 5×(8-2) = 30 kg m/s, time = 10 s, so average force = 30/10 = 3 N. Always check direction, but magnitude is 3 N.

This question belongs to: Science Physics
Question #2
Kepler's Second Law of planetary motion (Law of Areas) is a direct consequence of the conservation of:
A. Total Mechanical Energy
B. Kinetic Energy
C. Angular Momentum
D. Linear Momentum

Correct Answer: Option C


Explanation:
Kepler's Second Law states that the line joining a planet to the Sun sweeps out equal areas in equal intervals of time (areal velocity is constant). Because the gravitational force is a central force (acting strictly along the radius vector), it exerts zero torque on the planet. When net torque is zero, angular momentum is strictly conserved.

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Question #3
The magnetic field inside a long, straight, current-carrying solenoid is:
A. Uniform (same at all points)
B. Zero
C. Stronger at the ends than at the center
D. Directly proportional to the radius of the solenoid

Correct Answer: Option A


Explanation:
An ideal solenoid consists of tightly packed coils. When current passes through it, the magnetic field lines inside the solenoid are parallel straight lines. This indicates that the magnetic field is uniform in magnitude and direction at all points strictly inside the central region of the solenoid. The field strength is given by B = mu_0 * n * I.

This question belongs to: Science Physics