If the distance between a point charge and an infinitely large charge plate is increased by factor 2, the new force on the point charge will be

The figure shows three spherical and equipotential surfaces A, B and C around a point charge q. The potential difference V_A - V_B = V_B - V_C. If t₁ and t₂ are the distances between them, then

Two point charges, each of charge + q, are fixed at (+ a, 0) and (– a, 0). Another positive point charge q placed at the origin is free to move along the x-axis. The charge q at the origin in equilibrium will have

Assuming the sun to have a spherical outer surface of radius r, radiating like a black body at temperature t^oC, the power received by a unit surface, (normal to the incident rays) at a distance R from the centre of the sun is

Two rods A and B of different materials are welded together, as shown in the figure. If their thermal conductivities are K₁ and K₂, then the thermal conductivity of the composite rod will be

Three rods made of the same material and having the same cross-section have been joined as shown in the figure below. Each rod is of the same length. The left and right ends are kept at 0^oC and 90^oC, respectively. The temperature of the junction of the three rods will be

A rod, 1 m long, made of a material of thermal conductivity 420 W/m/K has one of its ends in melting ice and the other end in boiling water. If its cross-sectional area is 10 cm², then the amount of ice that melts in 1 minute is

A liquid takes 6 minutes to cool from 80^oC to 50^oC. If the temperature of the surroundings is 20^oC, then how long will it take to cool from 60^oC to 30^oC?