Physics
We use a concave polished metallic surface as a reflector in a torch to obtain a parallel beam of light. The position of the bulb is :
- at the centre of curvature of the reflector.
- at the focus of the reflector
- between the focus and centre of curvature of the reflector
- can be any of the above options
Answer
at the focus of the reflector
Reason — In a torch, we want the light rays to come out as a parallel beam as this helps the light travel a long distance in a specific direction and a concave mirror reflects light rays parallel to the principal axis if the source is placed at its focus.
So, if we want a parallel beam of light (which is the case in a torch), the bulb should be placed at the focus of the concave mirror.
Related Questions
Which mirror always forms a diminished image for all positions of the object placed in front of it ?
- plane mirror
- convex mirror
- concave mirror
- parabolic mirror
The figure shows the image of a clock as seen in the plane mirror. The correct time is :
- 4:30
- 6:30
- 2:30
- 3:30
Assertion (A) : For a ray of light incident at an angle of incidence i = 0°, angle of reflection is r = 0°.
Reason (R) : The angle of incidence i is equal to angle of reflection r.
- both A and R are true and R is the correct explanation of A
- both A and R are true and R is not the correct explanation of A
- assertion is false but reason is true
- assertion is true but reason is false
Assertion (A) : The image of an object placed close to a concave mirror is a real image.
Reason (R) : A real image is formed due to the actual intersection of the reflected rays.
- both A and R are true and R is the correct explanation of A
- both A and R are true and R is not the correct explanation of A
- assertion is false but reason is true
- assertion is true but reason is false