Light - TIR - Find the refractive index of the liquid

Answer: Option D

For total internal reflection TIR to occur, two conditions must be present:

1. light must be travelling from a optically denser medium towards an optically less dense medium.

2. the angle of incidence i is greater than the critical angle c

Key things to take note:

1. The angles stated on the diagram are not angles of incidence. Angle of incidence is between the incident ray and the normal.

2. The diagram on the left is TIR as all the light is being internally reflected within the optical denser medium, which is the liquid.

3. The diagram on the right with refracted ray along the boundary, i.e. angle of refraction is 90 degrees, the angle of incidence now is also the critical angle of the liquid.

Refer to the video explanation

Light - Total Internal Reflection (TIR) https://youtu.be/en3v38oof1Q

Find the energy dissipated by frictional forces when the car moves down from X to Y.

Answer: Option B

Using conservation of energy (COE), the total energy of the car at X = total energy at Y.

At X, the car only has gravitational potential energy. If there is no friction, the magnitude of the kinetic energy must be equal to the GPE at X.

But since there is frictional force, there will be some energy wasted as work done against friction, usually in the form of internal (thermal) energy and sound energy.

Hence, GPE at X = KE at Y + WD against friction

Refer to the video explanation

Find energy dissipated by frictional force when car moves down from X to Y https://youtu.be/gOihfTkUInE

Liquid Pressure - Determine the pressure of the enclosed air in the manometer (pure physics)

Answer: Option A

Refer to the video explanation

Liquid pressure - Pressure of enclosed air in the manometer https://youtu.be/APRx-ES-s3o