For a steel boat floating on a lake, the weight of the water displaced by the boat is

• less than the weight of the boat

• more than the weight of the boat

• equal to the weight of the part of the boat which is below the water level of the lake

• equal to the weight of the boat

282.

Which one among the following is not produced by sound waves in the air?

• Polarization

• Diffraction

• Reflection

• Refraction

A body attached to a spring balance weighs 10 kg on the Earth. The body attached to the same spring balance is taken to a planet where gravity is half that of the Earth. The balance will read

• 20 kg

• 10 kg

• 5 kg

• 2.5 kg

The resistance of a wire is 10 Ω. If it is stretched ten times, the resistance will be

• 1W

• 10 W

• 100 W

• 1000 W

If the focal length of the biconvex lens is 25 cm, then the power of the lens will be

• +4 dioptre

• -4 dioptre

• +0.04 dioptre

• -0.04 dioptre

A compound slab is composed of two parallel layers of different materials, with thickness 3cm and 2 cm. The temperatures of the outer faces of the compound slab are maintained at 100°C and 0°C. If conductivities are 0.36 and 0.16 then the temperature of the Junction is:

• 40°C

• 60°C

• 100°C

• 50%C

The torque on a rectangular coil placed in a uniform magnetic field is large when the

• number of turns are large

• number of turns is less

• plane of the coil is perpendicular to the magnetic field

• area of the coil is small

Two metallic wires A and B are of the same material and have equal lengths. If the cross-sectional area of B is double that of A, then which one among the following is the electrical resistance of B?

• Twice that of A

• 4 times that of A

• $\frac{1}{4}$ that of A

• $\frac{1}{2}$ that of A

Two thin lenses of focal lengths 20 cm and 25cm are placed in contact. The effection power of the combination is:

• 45 dioptres

• 9 dioptres

• $\frac{1}{9}$dioptres

• 6 dioptres

Two copper wires A and B length I and 2l respectively, have the same area of cross-section. The ratio of the resistivity of wire A to the resistivity of wire B is

• 4

• 2

• 1

• 1/2