Physics

Light and Mirrors

454 Questions

Light and mirrors questions cover the principles of reflection, image formation, and mirror magnification. Concepts include the properties of plane mirrors, the uses of concave mirrors in solar devices, and the behavior of light rays. These fundamentals are essential general science topics in major competitive examinations.

Plane mirror propertiesConcave mirror applicationsMirror magnification formulaLight reflection lawsImage formation

Light and Mirrors Questions

Multiple choice physics reflection of light at curved surfaces the mirror formula derivation of formula for curved mirrors mirror formula and magnification

A point object is placed at a distance $10cm$ and its real image is formed at a distance of $20cm$ from concave mirror. If the object is moved by $0.1cm$ towards the mirror, the image will shift by about

  1. $0.4cm$ away from the mirror
  2. $0.4cm$ towards the mirror
  3. $0.8cm$ away from the mirror
  4. $0.8cm$ towards the mirror
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

$We\quad know\quad \dfrac { 1 }{ f } =\dfrac { 1 }{ u } +\dfrac { 1 }{ v } ;\quad \ where\quad f=focal\quad length=?\ u=\quad initial\quad distance=20\quad cm\ v=\quad final\quad distance=10cm\ \dfrac { 1 }{ f } =\dfrac { 1 }{ -20 } +\dfrac { 1 }{ (-10) } \ f=\dfrac { 20 }{ 3 } \quad cm\ Now\quad object\quad moved\quad towards\quad the\quad mirror=0.1\quad cm,so\quad the\quad new\quad value\quad of\quad u=9.9\quad cm\ Again\quad \quad \quad \ \dfrac { 1 }{ f } =\dfrac { 1 }{ { u } _{ 1 } } +\dfrac { 1 }{ { v } _{ 1 } } \ \dfrac { 1 }{ f } -\dfrac { 1 }{ { u } _{ 1 } } =\dfrac { 1 }{ { v } _{ 1 } } \ \dfrac { 1 }{ { v } _{ 1 } } =\quad \dfrac { 3 }{ 20 } -\dfrac { 1 }{ (-9.9) } \ { v } _{ 1 }=20.4\quad cm\ The\quad change\quad in\quad final\quad distance\quad =20.4cm\quad -20\quad cm=0.4\quad cm\ \ v=\dfrac { 9\times 1600 }{ 3600 } =\quad 4cm/s$

Multiple choice physics reflection of light at curved surfaces the mirror formula derivation of formula for curved mirrors mirror formula and magnification

A plane mirror produces a magnification of

  1. $-1$
  2. $+1$

  3. Zero

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

The magnification produced by a plane mirror is $+1$ implies that the image formed by a plane mirror is virtual$,$

erect and of the same size$,$ as that of object$.$
Hence,
option $(B)$ is correct answer.

Multiple choice physics reflection of light at curved surfaces the mirror formula derivation of formula for curved mirrors mirror formula and magnification

If two mirrors are inclined at some angle $\theta$. An object is placed between the mirrors and there are 5 images formed for an object, then $\theta$ is may be

  1. $45^o$
  2. $53^o$
  3. $63^o$
  4. $75^o$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

The number of images formed by two mirrors at an angle $\theta $ is

$\begin{array}{l} n=\dfrac { { 360 } }{ \theta  } -1 \ \because n=5\, \, \left( { given } \right)  \ \therefore 5=\dfrac { { 360 } }{ \theta  } -1 \ \therefore \theta =\dfrac { { 360 } }{ 6 } ={ 60^{ 0 } } \end{array}$
Hence, the angle may be $63^0$.

Multiple choice physics reflection of light at curved surfaces the mirror formula derivation of formula for curved mirrors mirror formula and magnification

The relation between $u, v$ ( u is the object distance and v is the image distance )  and f for mirror is given by:

  1. $\displaystyle f=\frac{uv}{u-v}$
  2. $\displaystyle f=\frac{2u\times v}{u+v}$
  3. $\displaystyle f=\frac{u\times v}{u+v}$

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

$\dfrac{1}{u} +\dfrac{1}{v} = \dfrac{1}{f} $

or $\dfrac{u+v}{uv} = \dfrac{1}{f}$
or $f=\dfrac{uv}{u+v}$

Multiple choice physics reflection of light at curved surfaces the mirror formula derivation of formula for curved mirrors mirror formula and magnification

Mirror formula is valid for:

  1. Convex mirror

  2. Concave mirror

  3. Both A and B

  4. For lenses and mirrors
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation
Mirror formula is:
$\dfrac {1}{v} + \dfrac {1}{u} = \dfrac {1}{f}$
That is; $\dfrac {1}{\text {Object Distance}} + \dfrac {1}{\text {Image Distance}} = \dfrac {1}{\text {Focal length of the mirror}}$
This relationship is applicable for both concave and convex mirrors.
Multiple choice physics reflection of light at curved surfaces the mirror formula derivation of formula for curved mirrors mirror formula and magnification

Mirror formula can also be written as:

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

Focal length, $f = \dfrac {R}{2}$, where $R$ = radius of curvature

So, $\dfrac {1}{v} + \dfrac {1}{u} = \dfrac {1}{f}$ can be written as
$\Rightarrow \dfrac {1}{v} + \dfrac {1}{u} = \dfrac {2}{R}$

Multiple choice physics reflection of light at curved surfaces the mirror formula derivation of formula for curved mirrors mirror formula and magnification

Mark the incorrect statement regarding mirror formula.

  1. Values of known and unknown parameters can be used with their proper signs

  2. Sign of unknown parameter comes of its own after calculation

  3. Mirror formula is applicable for both concave and convex mirrors

  4. All
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

The values of known parameter should be used with their proper sign convention. No sign should be attached to the unknown parameter during calculation. Its sign will come of its own after calculation.

Multiple choice physics reflection of light at curved surfaces the mirror formula derivation of formula for curved mirrors mirror formula and magnification

The relation among u, v and f for a mirror is

  1. $f = uv/(u+v)$
  2. $v = fu/(u+f)$
  3. $u = fv/(f+v)$

  4. All of these
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

According to mirror equation.

$\cfrac{1}{f} = \cfrac{1}{u}+ \cfrac{1}{v}$
$\cfrac{1}{f} = \cfrac{u+v}{uv}$
$f = \cfrac{uv}{u+v}$

Similarly,
$v = \cfrac{fu}{u-f}$
$u = \cfrac{fv}{v-f}$

Multiple choice physics reflection of light at curved surfaces the mirror formula derivation of formula for curved mirrors mirror formula and magnification

The relation among $u,v$ and $f$ for a mirror is:

  1. $f=uv(u+v)$
  2. $v=fu(u+f)$
  3. $u=fv(f+v)$

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

from mirror formula

              $\dfrac { 1 }{ v } +\dfrac { 1 }{ u } =\dfrac { 1 }{ f } $
              $\Rightarrow \quad \boxed { f=\dfrac { uv }{ u+v }  } $
and
          $1+\dfrac { v }{ u } =\dfrac { v }{ f } \Rightarrow \boxed { u=\dfrac { fv }{ f-v }  } $

Multiple choice evs magic with mirrors kaleidoscope uses of plane mirror reflected light can be reflected again

What is Kaleidoscope?

  1. A cylinder with mirrors containing loose colored objects such as beads, pebbles, and bits of glass

  2. A cylinder with mirrors

  3. A cylinder containing loose colored objects such as beads, pebbles, and bits of glass

  4. None of the above
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

$Answer:-$ A option

A kaleidoscope is an optical instrument, typically a cylinder with mirrors containing loose, colored objects such as beads or pebbles and bits of glass. As the viewer looks into one end, lightening the other end creates a colorful pattern, due to repeated reflection in the mirrors.

Multiple choice evs magic with mirrors kaleidoscope uses of plane mirror reflected light can be reflected again

An object is kept between two plane mirrors inclined at an angle $120$ from each other; calculate the number of images which are formed if the object is not on the bisector/on the bisector $3$

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

Given: An object is kept between two plane mirrors inclined at an angle 120 from each other

To find the ratio of number of images which are formed if the object is not on the bisector and on the bisector
Solution:
If there are two plane mirrors inclined to each other at an angle $\theta$, the number of images of a point object formed are determined as follows:

If $\left(\dfrac {360^\circ}\theta\right)$ is odd integer (say $m$) number of images formed
$n = m$, if the object is not on the bisector of mirrors
$n = (m – 1)$, if the object is on the bisector of mirrors.

So, when $\theta=120^\circ$, we get
$m=\dfrac {360}{120}=3$
So,
$\dfrac {\text{ number of images which are formed if the object is not on the bisector}}{\text{ number of images which are formed if the object is on the bisector}}=\dfrac {3}{3-1}=\dfrac 32$