Electric Charges and Fields — Physics STD 12 Science — Question

Four 2cm × 2cm × 2cm cubes of ice are taken out from a refrigerator and are put in 200ml of a drink at 10°C.

1. Find the temperature of the drink when thermal equilibrium is attained in it.
2. If the ice cubes do not melt completely, find the amount melted. Assume that no heat is lost to the outside of the drink and that the container has negligible heat capacity. Density of ice = 900kg-m^-3, density of the drink = 1000kg-m^-3, specific heat capacity of the drink = 4200Jkg^-1-K^-1, latent heat of fusion of ice = 3.4 × 10⁵J-kg^-1.

There is a potential of 10V on the surface of a charged spherical shell of radius 10 cm. Write the value of potential at a distance of 5 cm from its centre.

When a body is weighed on an ordinary balance we demand that the arm should be horizontal if the weights on the two pans are equal. Suppose equal weights are put on the two pans, the arm is kept at an angle with the horizontal and released. Is the torque of the two weights about the middle point (point of support) zero? Is the total torque zero? If so, why does the arm rotate and finally become horizontal?

At an airport, a person is made to walk through the doorway of a metal detector, for security reasons. If she/he is carrying anything made of metal, the metal detector emits a sound. On what principle does this detector work?

Who first of all gave experimental evidence of existence of electromagnetic waves?

Two proton beams going in the same direction repel each other whereas two wires carrying currents in the same direction attract each other. Explain.

What is doping?

Give the ratio of number of holes and number of conduction electrons in an intrinsic semiconductor.