Soap helps in cleaning clothes, because

1. It attracts the dirt particles

2. It decreases the surface tension of water

3. It increases the cohesive force between water molecules

4. It increases the angle of contact

On increasing temperature of a liquid, its surface tension generally

1. Increases

2. Decreases

3. Remains constant

4. First increases and then decreases

The raincoats are made water proof by coating it with a material, which

1. Absorb water

2. Increase surface tension of water

3. Increase the angle of contact

4. Decreases the density of water

An iron needle slowly placed on the surface of water floats because

1. It displaces water more than its weight

2. The density of material of needle is less than that of water

3. Of surface tension

4. Of its shape

Two water droplets merge with each other to form a larger droplet. In this process

1. Energy is liberated

2. Energy is absorbed

3. Energy is neither liberated nor absorbed

4. Some mass is converted into energy

The radius of a soap bubble is r. The surface tension of soap solution is 'S'. Keeping temperature constant, the radius of the soap bubble is soubled. The energy necessary for this will be

1. $24 {\mathrm{\pi r}}^2\mathrm{S}$

2. $8 {\mathrm{\pi r}}^2\mathrm{S}$

3. $16 {\mathrm{\pi r}}^2\mathrm{S}$

4. $12 {\mathrm{\pi r}}^2\mathrm{S}$

The surface tension of a liquid is 5 N/m. If a film is held on a ring of area 0.02 m², its surface energy is about

1. $5\times {10}^{-2} \mathrm{J}$

2. $2.5\times {10}^{-2} \mathrm{J}$

3. $2\times {10}^{-1} \mathrm{J}$

4. $3\times {10}^{-1} \mathrm{J}$

Two soap bubbles having radii 3 cm and 4 cm in vacuum, coalesce under isothermal conditions. The radius of the new bubble is

1. 1 cm

2. 5 cm

3. 7 cm

4. 3.5 cm

The work done to break a spherical drop of radius R in n drops of equal size is proportional to

1. $\frac{1}{{\mathrm{n}}^{2/3}}-1$

2. $\frac{1}{{\mathrm{n}}^{1/3}}-1$

3. ${\mathrm{n}}^{1/3}-1$

4. ${\mathrm{n}}^{4/3}-1$

The kerosene oil rises up in the wick of a lamp

1. Due to high surface tension of coil

2. Because the wick attracts the oil

3. Because the wick decreases the surface tension of oil

4. Due to capillaries formed in the wick