Physics MCQs for NEET — Practice Questions with Answers

Writing on a blackboard with a piece of chalk is possible due to adhesive forces. Adhesive forces are the attractive forces between unlike substances, such as chalk and the blackboard. These forces enable the chalk particles to stick to the surface of the blackboard, allowing writing to occur. Therefore, option o1 is correct.

When there is no external force acting on a liquid drop, its shape is determined by surface tension. Surface tension is the property of the liquid that causes it to acquire the least surface area possible, resulting in a spherical shape for the drop. Therefore, option o1 is correct.

Soap helps in cleaning by lowering the surface tension of water. This allows the water to spread more easily and interact with oils and dirt, emulsifying them and making them easier to rinse away.

Soap helps to lower the surface tension of solution thus soap get stick to the dist partcles and grease and these are removed by action of water.

When a square frame of side L is dipped in a liquid and a membrane is formed, the force due to surface tension acting on the frame can be calculated using the formula: \(F = 4TL\), where T is the surface tension and L is the length of one side of the square. However, since there are two surfaces (top and bottom of the membrane), the total force is \(8TL\).

Force required to separate the plates $ = { 2TA \over t } $

When a metal disc floats on the water surface, the surface tension acts along the perimeter of the disc. The vertical component of this force balances the weight of the disc. Hence, the weight of the metal disc is given by the sum of the vertical component of the surface tension force and the weight of the displaced water. Therefore, the correct expression is $2 \\pi r T \\cos heta + W$.

$ w = 8 \pi T ( R_2^2 - R_1 ^2 ) = 8 \pi T ( (2r)^2 - (r)^2 ) = 24 \pi r^2 T $

$ Energy spent = T \times increase in surface ared$ $ = T \times 2 ( 4 \pi ( 2r)^2 - 4 \pi r^2 ) = ( 24 \pi T r^2) joule $