Fermat's Theorem

Q.

What does these lines mean- the fact that a small source of light casts a sharp shadow of an opaque object points to this straight line path of light, usually indicated as a ray of light.

Q.

A source of light which is of the size of ________ is called a point source of light.

Q.

A source of light which is larger than a point source of light is called?

1. bigger source of light

2. larger source of light

3. extended source of light

4. none of the above

Q. Two plane mirrors are arranged at right angles to each other as shown in figure. A ray of light is incident on the horizontal mirror at an angle θ. For what value of θ does the ray emerge parallel to the incoming ray after reflection from the vertical mirror?

1. 45°
2. 25°
3. 75°
4. All of these

Q. What are the laws of reflection?

Q. Pick the mirror with the widest field of view.

1. Convex mirror
2. Cylindrical mirror
3. Plane mirror
4. Concave mirror

Q.

When an extended source of light moves towards a stationary opaque body, where the extended source is bigger than the opaque body, then on a stationary screen placed behind the object the

1. penumbra and umbra, both decreases

2. penumbra and umbra, both increases

3. penumbra increases and the umbra decreases

4. penumbra decreases and the umbra increases

Q.

A ray of light always travels in a straight line, because:
A. Straight line path has the least distance.
B. Straight line path takes the least time.
Select the correct explanation.

1. A only

2. B only

3. Both A and B

4. None of the above

Q. Light always takes the shortest path

1. False
2. True

Q.

Statement 1: Angle of incidence is always equal to the angle of reflection.

Statement 2: Angle of incidence is always twice the angle of reflection.

Statement 3: The incident ray, reflected ray and the normal all lie in 3 different planes.

Statement 4: The incidence ray, reflected ray and the normal all lie in the same plane.

Which of the statements refer to the laws of reflection?

1. 2 & 4

2. 1 & 4

3. 2 & 3

4. 1 & 3

Q. Assume the distance between the sun and the mirror is infinity and the sun is much above the principal axis. Where will the image of the sun be formed?

1. Ar the focal point
2. In the focal plane but below the principal axis
3. In the focal plane but below the principal axis
4. At center of curvature

Q. Both refraction and reflection follow Fermat's Law.

1. False
2. True

Q. Fermat's principle is not valid for a medium whose density varies continuously.

1. True
2. False

Q. The Laws of Reflection are applicable even if the incident ray and the reflected ray are in same plane and the normal is in a different plane:

1. False
2. True

Q. The incident ray, reflected ray and the normal in case of a plane mirror are in the ..............

1. Same plane
2. None of the above
3. Different planes
4. Parallel planes

Q. A ray of light always travels in a straight line, because:
A. Straight line path has the least distance.
B. Straight line path takes the least time.
Select the correct explanation.

1. None of the above
2. B only
3. Both A and B
4. A only

Q. Fermat's principle is not valid for a medium whose density varies continuously.

1. True
2. False

Q. The laws of reflection hold good for :

1. plane mirror only
2. concave mirror only
3. all mirrors irrespective of their shape
4. convex mirror only