Explanation

• Heat transfer by conduction depends on thermal conductivity of material.
• Copper is a very good conductor of heat, while glass is a poor conductor.
• Both rods have same length and same temperature difference.
• So the deciding factor is only thermal conductivity (k).
• Higher k → faster energy transfer.

Last verified on 22-05-2026

Explanation

• Internal energy is the total microscopic energy of gas molecules.
• In an ideal gas, only kinetic energy of molecules is considered.
• So it depends only on temperature.
• Higher temperature means higher internal energy.

Last verified on 22-05-2026

Explanation

• In β⁻ decay, a neutron converts into a proton.
• So, the number of protons increases by 1.
• Therefore, atomic number Z increases by 1.

Last verified on 22-05-2026

Explanation

Kinetic energy gained by electron:

KE = eV

For 150 V:

KE = 150 eV

In joules:

1 eV = 1.6 × 10⁻¹⁹ J

KE = 150 × 1.6 × 10⁻¹⁹ J

Last verified on 22-05-2026

Explanation

• An equipotential surface has the same electric potential everywhere.
• No potential difference exists between any two points on it.
• Work done depends on potential difference.
• If potential difference is zero, work done is also zero.
• So moving charge on it requires no energy.

Last verified on 22-05-2026

Explanation

• A conductor contains free electrons that can move freely.
• In electrostatic equilibrium, charges stop moving.
• If any electric field existed inside, charges would move.
• So charges rearrange themselves until internal field cancels out.
• Hence, no net electric field remains inside.

Last verified on 22-05-2026

Explanation

When lenses are placed in contact, their powers add:

P = P₁ + P₂ = +2 D + (-5 D) = -3 D

Focal length f in meters is f = 1/P:

f = 1/(-3) = -0.33 m

So the equivalent power is -3 D and the equivalent focal length is -0.33 m.

Last verified on 22-05-2026

Explanation

For a black body, radiated energy per unit time per unit area follows Stefan-Boltzmann law:

E ∝ T⁴

Temperature goes from 400 K to 800 K, so it doubles: 800/400 = 2.

New energy = (2)⁴ × original energy = 16 × original energy.

Last verified on 22-05-2026

Explanation

For light passing from a medium to air, the critical angle is given by:

sin θc = 1/n

Here n = 1.5, so  

sin θc = 1/1.5 = 0.6667  

θc = arcsin(0.6667) ≈ 41.8°

Last verified on 22-05-2026

Explanation

For masses m and 3m over a frictionless pulley, the heavier mass pulls the system down. 

Net pulling force = 3mg - mg = 2mg  

Total mass being moved = m + 3m = 4m  

So acceleration a = net force / total mass = 2mg / 4m = g/2.

Thus the system accelerates at g/2, with 3m going down and m going up.

Last verified on 22-05-2026