Define the term, ‘Critical Angle’. What is meant by ‘total internal reflection’? State two essential conditions for total internal reflection to take place. With the help of a ray diagram, illustrate an application of total internal reflection. OR (a) What is meant by a ‘magnetic field’? (b) How is the direction of magnetic field at a point determined? (c) Describe an activity to demonstrate the direction of the magnetic field generated around a current carrying conductor. (d) What is the direction of magnetic field at the centre of a current carrying circular loop?