Physics

Light and Mirrors

458 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 problems on mirror and magnification formula derivation of formula for curved mirrors mirror formula and magnification

An object is placed in front of a concave mirror of radius of curvature 15 cm, at a distance of 10 cm, the position and nature of the image formed is :

  1. $+30 cm, virtual \ and \ erect$
  2. $+30 cm, real \ and \ inverted$
  3. $-30 cm, virtual \ and \ erect$
  4. $-30 cm, real \ and \ inverted$
Reveal answer Fill a bubble to check yourself
D Correct answer
Multiple choice physics reflection of light at curved surfaces problems on mirror and magnification formula derivation of formula for curved mirrors mirror formula and magnification

Mark the correct statement(s) w.r.t. a concave spherical mirror

  1. for real extended object, it can form a diminished virtual image

  2. for real extended object, it can form a magnified virtual image

  3. for virtual extended object, it can form a diminished real image

  4. for virtual extended object, it can form a magnified real image
Reveal answer Fill a bubble to check yourself
B,C Correct answer
Explanation
$\dfrac{1}{v}+\dfrac{1}{u}=\dfrac{1}{f}$

$v= \dfrac{fu}{u-f}$

magnification is $\dfrac{-v}{u}=\dfrac{f}{f-u}$

if $f>|u|$ (u<0) then a magnified image is formed which is virtual 

if $u>2f$ (u>0) then a diminished image is formed which is real 

option $B,C$ are correct
Multiple choice physics reflection of light at curved surfaces problems on mirror and magnification formula derivation of formula for curved mirrors mirror formula and magnification
If linear magnification for a spherical mirror is $\dfrac{3}{2}$, then we may write: (symbols have their usual meanings) 
  1. $f=\dfrac{u}{2}$
  2. $f=\dfrac{3u}{2}$
  3. $f=\dfrac{3u}{5}$

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

Mirror equation is: $\dfrac{1}{f}=\dfrac{1}{v}+\dfrac{1}{u}$

Multiplying both sides by $u$, we get:
$\dfrac{u}{f}=\dfrac{u}{v}+1$
Or  $\dfrac{u}{v}=\dfrac{u}{f}-1=\dfrac{u-f}{f}$
Or  $\dfrac{v}{u}=\dfrac{f}{u-f}$
Now, magnification, $m=\dfrac{v}{u}=\dfrac{3}{2}$
$\therefore$ $\dfrac{f}{u-f}=\dfrac{3}{2}$
Solving the above equation we get  $\dfrac{5}{2}f=\dfrac{3}{2}u$
 $\implies f=\dfrac{3u}{5}$

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

If magnification is positive, the nature of the image is:

  1. real and inverted

  2. virtual and erect

  3. real

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

$\text{Magnification}=\dfrac{\text{Image  size}}{\text{Object  size}}$

According to new Cartesian sign convention, size of height of real and inverted image is considered negative and that of virtual and erect image is considered positive.
The heigh of the object, being erect is considered positive always.
So, for positive magnification, the ratio, mentioned above, will be positive. This implies that the image height will also be positive.
The image will be virtual and erect.

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

A concave mirror is made from a hollow sphere of radius of curvature 30 cm.  If an object of height 2 cm is placed at 10 cm from the pole of the mirror, determine the size of the image :

  1. 3 cm

  2. 6 cm

  3. 12 cm

  4. 24 cm
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Given: $u=-10cm$


$f=-15cm$

$h _{o}=2cm$

To find, $h _{o}$

From mirror formula,

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

$\dfrac{1}{v}-\dfrac{1}{10}=-\dfrac{1}{15}$

$\dfrac{1}{v}=\dfrac{1}{10}-\dfrac{1}{15}=\dfrac{5}{150}$

$v=30cm$

$magnification=\dfrac{h _{i}}{h _{o}}=\dfrac{-v}{u}$

$\dfrac{h _{i}}{2}=\dfrac{-30}{-10}$

$h _{i}=6cm$

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

A concave mirror produces $2$ times magnified real image of an object placed at $5 cm$ in front of it. Where is image located?

  1. $10 cm$
  2. $-5 cm$
  3. $-10 cm$
  4. $2.5 cm$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Magnification, $m = \dfrac {-v}{u}$
Given, magnification, $m = -2$

$-2 = \dfrac {-v}{-5 cm}$
Therefore, object distance, $v = -2\times 5 cm = -10 cm$

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

Magnification produced by plane mirror is $+1$. It means:

  1. Image formed by plane mirror is greater than size of the object

  2. Image formed by plane mirror is erect and of same size as the object

  3. Image formed by plane mirror is smaller than size of object and is virtual

  4. None
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Magnification $= +1$ signifies that the image formed in a plane mirror is of same size as the object. Positive sign in the value of magnification signifies that image formed by a plane mirror is erect.

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

The radius of curvature of concave mirror is 24 cm and the image is magnified by 1.5 times. The object distance is

  1. 20 cm

  2. 8 cm

  3. 16 cm

  4. 24 cm
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Given that, $\displaystyle R=-24$cm
$\displaystyle f=-12cm$ and $\displaystyle m=1.5$
By the lens formula,
$\displaystyle \frac { 1 }{ v } +\frac { 1 }{ u } =\frac { 1 }{ f } $
$\displaystyle \frac { 1 }{ 1.5u } +\frac { 1 }{ u } =-\frac { 1 }{ 12 } $
$\displaystyle \frac { 2.5 }{ 1.5u } =-\frac { 1 }{ 12 } $
or, $\displaystyle u=-20cm$

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

We want a mirror that will make an object look larger. What combination of image and object distances (from the mirror) will accomplish this?

  1. Image Distance $3.0 cm$, Object Distance $3.0 cm$
  2. Image Distance $2.0 cm$, Object Distance $3.0 cm$
  3. Image Distance $3.0 cm$, Object Distance $5.0 cm$
  4. Image Distance $3.0 cm$, Object Distance $2.0 cm$
  5. Image Distance $3.0 cm$, Object Distance $10.0 cm$
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Magnification by a mirror         $m = \dfrac{-v}{u}$


For option D :    $m = \dfrac{- 3.0}{-2.0} = 1.5$             $\implies m>1$
Thus the data given in option D will make a larger image.

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

The magnification produced by a mirror is $+\dfrac{1}{3}.$ Then the mirror is a ____________.

  1. Concave mirror

  2. Convex mirror

  3. Plane mirror

  4. plano convex mirror
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

The image produced is virtual and erect and also diminished.


Hence, the mirror must be $convex$ mirror. Concave mirror also produces virtual image but it is enlarged.But convex mirror always produces diminished virtual image.

Answer-(B)

Multiple choice evs - i substances, objects and energy renewable and non-renewable resources renewable and non-renewable sources of energy solar energy and its applications renewable resources alternative fuels and energy sources alternative sources of energy

Which of the following statements about pinhole camera are correct?
(i) It is a camera with a single lens.
(ii) It produces an upside down image of object.
(iii) It does not have a screen.
(iv) It works because light travels in a straight line.
(v) It forms real and colourless shadows of objects.

  1. (i) and (v) only

  2. (ii) and (iv) only

  3. (i), (iii) and (iv) only

  4. (ii), (iv) and (v) only
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

A pinhole camera is a simple camera without a lens but with a tiny aperture. A pinhole is effectively a light proof box with a small hole in one side. Light from a scene passes through the aperture and projects an invested image on the opposite side of the box.
The image of a pinhole camera may be projected onto a translucent screen for real time viewing.