Tag: reflection of light in spherical mirrors

Quizzes (8) Questions (84)

Questions Related to reflection of light in spherical mirrors

Multiple choice physics reflection of light in spherical mirrors focus and focal length spherical mirror formula and magnification reflection of light by curved surfaces

The distance at which an object should be placed in front of a convex lens of focal length 10 cm to obtain a real image double the size of object will be:

  1. 30 cm

  2. 15 cm

  3. 5 cm

  4. 10 cm
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Convex lens gives the real and double-sized image when the object is placed exactly between the focus and radius of curvature.
We have, $\displaystyle \frac{1}{f} = \frac{1}{v} - \frac{1}{u}$
$m = \displaystyle \frac{v}{u} = 2$ or $v = 2u$


$\therefore \displaystyle \frac{1}{f} = \frac{1}{2u} - \frac{1}{-u} = \frac{1}{2u} + \frac{1}{u} = \frac{3}{2u}$

or $\displaystyle \frac{1}{10} = \frac{3}{2u}$ or $u = 15 cm$

Multiple choice physics reflection of light in spherical mirrors focus and focal length spherical mirror formula and magnification reflection of light by curved surfaces

An object is placed at the centre of curvature of a concave mirror of radius of curvature $20$cm. The nature and position of the image shall be.

  1. Virtual and $15$cm from the mirror
  2. Real and $20$cm from the mirror
  3. Virtual and $20$cm from the mirror
  4. Real and $10$cm from the mirror
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Image of an object placed at center of curvature is inverted, real and of the same size and is formed at the center of curvature. Hence image will be real and at the center of curvature (20 cm from mirror).

Multiple choice physics reflection of light in spherical mirrors focus and focal length spherical mirror formula and magnification reflection of light by curved surfaces

Formula of focal length in convex lens is

  1. $\displaystyle f = \frac{u+v}{u-v}$
  2. $\displaystyle f = \frac{u\times v}{u-v}$
  3. $\displaystyle f = \frac{u-v}{u+v}$
  4. $\displaystyle f = \frac{u+v}{u+v}$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

The standard lens formula is 1/v - 1/u = 1/f. Solving for f gives f = (uv) / (u - v).

Multiple choice physics reflection of light in spherical mirrors focus and focal length spherical mirror formula and magnification reflection of light by curved surfaces

An object is placed at a distance of $50\ cm$ from a convex mirror. A plane mirror is placed in front of the convex mirror in such a way that it covers half of the convex mirror. If the distance between object and plane mirror is $30\ cm$ then there is no parallax between the images formed by two mirrors, the radius of curvature of convex mirror will be :

  1. $50\ cm$
  2. $25\ cm$
  3. $12.5\ cm$
  4. $100\ cm$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

For the plane mirror, the image is formed 30 cm behind it. For the convex mirror, the object is at 50 cm. No parallax means the images coincide. This setup requires calculating the focal length based on the image position.

Multiple choice physics reflection of light in spherical mirrors sign convention for mirrors sign convention for spherical mirrors sign convention for the measurement of distances

Magnification produced by a convex mirror is $\frac { 1 }{ 3 }$, then distance of the object from mirror is

  1. $\frac { f }{ 3 }$
  2. $\frac { 2f }{ 3 }$
  3. $1f$
  4. $2f$
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Magnification m = -v/u = 1/3 for a convex mirror. Using the mirror formula 1/v + 1/u = 1/f, we substitute v = -u/3. This gives -3/u + 1/u = 1/f, leading to -2/u = 1/f, so u = -2f. The distance is 2f.

Multiple choice physics reflection of light in spherical mirrors sign convention for mirrors sign convention for spherical mirrors sign convention for the measurement of distances

A convex lens of focal length 30 cm forms an image of height 2 cm for an object situated at infinity. If a concave lens of focal length 20 cm is placed coaxially at a distance of 26 cm in front of convex lens. then size of final image would be:

  1. $1.25cm$
  2. $2.5 cm$
  3. $2 cm$
  4. $0.75cm$
Reveal answer Fill a bubble to check yourself
B Correct answer
Multiple choice physics reflection of light in spherical mirrors sign convention for mirrors sign convention for spherical mirrors sign convention for the measurement of distances

The object distance $u$ for a concave mirror:

  1. must be positive

  2. must be negative

  3. must not be negative

  4. may be negative
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Positive and negative sign depend on the assumption of sign conversion.
either side we can consider positive or negative.
Hence Option D.

Multiple choice physics reflection of light in spherical mirrors sign convention for mirrors sign convention for spherical mirrors sign convention for the measurement of distances

The linear magnification for a mirror is the ratio of the size of the image to the size of the object, and is denoted by m. Then m is equal to (symbols have their usual meanings).

  1. $\displaystyle \frac { uf }{ u-f } $
  2. $\displaystyle \frac { uf }{ u+f } $
  3. $\displaystyle \frac { f }{ u-f } $

  4. None of these
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

we now,$\dfrac{1}{f}=\dfrac{1}{v}+\dfrac{1}{u}$
multiplying by u in above eq.
$\dfrac{u}{f}=\dfrac{u}{v}+\dfrac{u}{u}$
$\dfrac{u}{f}=\dfrac{u}{v}+1$
$\dfrac{u}{f}-1=\dfrac{u}{v}$
$\dfrac{u}{v}=\dfrac{u-f}{f}$
$\dfrac{v}{u}=\dfrac{f}{u-f}  ,  As, m=\dfrac{v}{u}$
$m=\dfrac{f}{u-f}$
hence,option C is correct.