Question

All rays that are parallel to the principle axis in a concave mirror reflects Select one: O a. Towards the focal point O b. Away from the focal point O c. Away from the center of curvature O d. Towards the center of curvature

Answer 1

1. All rays that are parallel to the principle axis in a concave mirror reflects

a. Towards the focal point

EXPLANATION:

The basic laws of reflection are the same for both the plane surface and the curved surface. On curved surface, we first draw a tangent at a point and then draw a perpendicular to that tangent at that point. Then we can define the angle of incidence and angle of reflection from this normal. The normal always a line that join center of curvature and the point of incidence of the ray. The angle of incidence and the angle of reflection are equal to each other. The incident ray, the normal, and the reflected ray are in the same plane.
For any spherical mirror, we can see that the focal point situated in between the pole and center of curvature of the spherical mirror. So when several parallel rays ( parallel to the principal axis) incident on the concave mirror, they must obey the law of reflection, and all reflected rays converge or meet to a particular point, which is known as a focal point. It is experimentally proved. That is why reflected rays from the concave mirror converges to its focal point.

2. The statements that are true about the virtual image are

a. A concave lens always form a virtual image.

EXPLANATION: Because the all rays diverge from the concave lens, they never converge. Therefore it seems that the emerge rays appear to converge. So a concave lens always form a virtual image.

c. A plane mirror always form a virtual image.

EXPLANATION: Because the reflected ray from the plane mirror always diverge, and they can not converge anyway. so it seems that the reflected rays appear to come from a point behind the mirror. That is why A plane mirror always form a virtual image.

e. It can not be viewed on a screen.

EXPLANATION: Because virual image form virtually, i.e, virtual image seems to appear from a point not originated in real. That is why we can not viewed the virtual image on a screen.

Option (b) and (d) can not be true. Option (b) can not be true because virtual images can be photographed. Because camera is made of lens through which we can capture both the real and virtual images of the object. Option (d) can not be true because eye act as a lens. so we can see the virtual image directly.

3. The focal length is equal to the

c. Half the radius of the curvature.

EXPLANATION: The formula of lens is

$\frac{1}{v}+\frac{1}{u}=\frac{1}{f}=\frac{2}{R}$

Where v= image distance

u= object distance

f= focal length

R= radius of curvature.

so, f= R/2

4. Virtual image is

d. From which light rays diverge but do not pass through.

EXPLANATION: From the definition of virtual image the light ray appear to diverge from a point but in real they are not pass through it.

5. The distace from the center of the mirror, c to the pole of the mirror is given as

b. 2f

EXPLANATION: We know, 1/f= 2/R

Therfore R =2f. R= distance betwwen c and pole of the mirror.

6. An image that is formed at the back of the mirrror is said to be

a. Virtual image.

EXPLANATION: Virtual image always form at the back of the mirror and the real image always form infront of the mirror.