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 in spherical mirrors sign convention for mirrors sign convention for spherical mirrors sign convention for the measurement of distances

A small candle 2.5 cm in size is placed 27 cm in front of a concave mirror of radius of curvature 36 cm.

  1. The distance from the mirror, should a screen be placed in order to receive a sharp image is-54 cm.

  2. The nature of image is virtual inverted w.r.t. object.

  3. The image formed is 8 times highest the object.

  4. The image formed is 3 times highest the object.
Reveal answer Fill a bubble to check yourself
A 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

An object is placed at a distance of 36 cm from a convex mirror . A plane mirror is placed in between , so that the two virtual image so formed coincide . If the plane mirror is at a distance of 24 cm from the object , find the radius of curvature of the convex mirror . 

  1. $43 cm$
  2. $36 cm$
  3. $78 cm$
  4. $97 cm$
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

A point object is placed at a distance of  $10\mathrm { cm }$  and its real image is formed at a distance of  $30\mathrm { cm }$  from a concave mirror. If the object is moved by  $0.2\mathrm { cm }$  towards the mirror. the image will shift by about.

  1. $1.8\mathrm { cm }$ away from the mirror
  2. $0.4\mathrm { cm }$ towards the mirror
  3. $0.8\mathrm { cm }$ away from the mirror
  4. $0.8\mathrm { cm }$ towards the mirror
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

Which one of the following has a negative sign, on the basis of new Cartesian sign Convention?

  1. Image distance for a convex mirror

  2. Height of a virtual and erect image

  3. Focal length of a convex mirror

  4. Object distance for a concave mirror
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

According to new Cartesian sign convention, object distance for any lens or mirror is measured as negative. This is because, the object distance is measured against the direction of incident light.

So, for the given options, object distance for a concave mirror has a negative sign.

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

Which of the following statements is correct according to New Cartesian Sign Convention?

  1. Focal length of a concave mirror is positive and that of a convex mirror is negative.

  2. Focal length of a concave mirror is negative and that of a convex mirror is positive.

  3. Image distance is always positive for a concave mirror.

  4. The height of all the real and inverted images is positive.
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

The focal length of a concave mirror, with a real focus, is always positive as is measured against the direction of incident light.

The focal length of a convex mirror, with a virtual focus, is always negative as is measured along the direction of the incident light.

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) For concave mirror focal length is taken as ........
b) For convex mirror, radius of curvature is taken as ........

  1. $a = positive, b = negative$
  2. $a = negative, b = positive$
  3. $a = positive, b = positive$
  4. $a = negative, b = negative$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

According to cartesian system focal length of a concave mirror is negative whereas radius of curvature of convex mirror is positive.

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 $2.0\ cm$ long object is placed perpendicular to the principal axis of a concave mirror. The distance of the object from the mirror is $30\ cm$, and its image is formed $60\ cm$ from the mirror, on the same side of the mirror as the object. Find the height of the image formed :

  1. $3\ cm$
  2. $4\ cm$
  3. $5\ cm$
  4. $8\ cm$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Distance of object from the mirror, $u=-30$ 


Distance of image from the mirror, $v=-60$ , image is real.


Now we know  magnification ratio $m=-\dfrac{v}{u}$

$m=-\dfrac{-60}{-30}$

$m=-2$

Height of object $h=2 cm$

Image height $h _1=m\times h=-2\times 2=-4cm$

Height of image is 4 cm and its inverted .

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

In a car a rear view mirror having a radius of curvature 1.50 m forms a virtual image of a bus located 10.0 m from the mirror. The factor by which the mirror magnifies the size of the bus is close to

  1. 0.06

  2. 0.07

  3. 0.08

  4. 0.09
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

R=1.5, u=$-10$

$\dfrac{2}{R}=\dfrac{1}{v}+\dfrac{1}{u}$
$v=\dfrac{30}{43}$
$m=\dfrac{-v}{u}=.069=.07$

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

An object is kept on the principal axis of a concave mirror of focal length $10$cm, at a distance of $15$cm from its pole. The image formed by the mirror is?

  1. Virtual and magnified

  2. Virtual and diminished

  3. Real and magnified

  4. Real and diminished
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Focal length of concave mirror  $f = -10 \ cm$
Object distance   $u = -15 \ cm$
Using     $\dfrac{1}{v}+\dfrac{1}{u} = \dfrac{1}{f}$
$\therefore$   $\dfrac{1}{v}+\dfrac{1}{-15} = \dfrac{1}{-10}$
$\implies   \ v = -30 \ cm$
Since $v$ is negative, so image formed is real.
Magnification  $m = \dfrac{-v}{u}$
$\therefore$  $m = -\dfrac{(-30)}{-15} = -2$
Since $m$ is greater than $1$, so magnified image is formed.
Correct answer is option C.

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

From the understanding of cartesian sign convention for reflection by spherical mirror,  students took part in group discussion for FA - 1 in classroom. Who is wrong in the group discussion?
Alpesh : All the distances are measured from the pole of a mirror parallel to the principal axis.
Beena : The distances measured in the direction of incident ray are taken positive.
Chamak : The height measured upward and perpendicular to principal axis is taken negative.
Daksha : The height measured downward and perpendicular to principal axis is taken as positive.

  1. Champak and Daksha

  2. Only Champak

  3. Alpesh and Beena

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

1- It is true that all the distances are measured from the pole of a mirror parallel to the principal axis.So, Alpesh is right.

2-It is also true that the distances measured in the direction of incident ray are taken positive.So, Beena is also right
3-The height measured upward and perpendicular to principal axis is taken positive. So, Chamak is wrong.
4-The height measured downward and perpendicular to principal axis is taken as negative.So, Daksha is also wrong.
So, only Champak and Daksha are wrong.
Therefore, A is correct option.

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 nature of image of a candle flame located $40$cm from a concave spherical mirror is real, inverted and magnified four times. Then the radius of curvature of the mirror is:

  1. $32$ cm
  2. $64$ cm
  3. $48$ cm
  4. $80$ cm
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Distance of the Candle from the Concave Mirror (u) = $40 cm$.(negative)

Now, as per as the Question,

$Image Height = 4 × Object (or Candle) Height$

 $Image Height/Candle Height = 4$

 Magnification = $4$

[ Magnification = Image Height/Object Height]

Now, Magnification = $-v/u$

 $4 = -v/u$

 $-v = 4u$

 $v = -4u$

 $v = -4 \times 40$

 $v = -160 cm.$

Now, Image Distance(v) = - $160 cm.$

Using the Mirror's Formula,

 On Multiplying both sides by $160$ ,

We get,

⇒  $160/f = -1 - 4$

⇒ $160/f = -5$

⇒ $f = 160/-5$

⇒ $f = -32 cm$.

∴ Focal length of the Concave Mirror is 32 cm.

Now, For the Radius of the Curvature,

Using the Formula,

 $ Focal Length = Radius Of Curvature/2$

∴ $Radius of Curvature = Focal Length \times 2$

∴ $R = F \times 2$

∴ $R = 32 \times 2$

∴ $R = 64 cm.$

Hence, the Radius of the Curvature of the Concave mirror of Focal Length 3 cm is 64 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

A convex mirror used for rear view on an automobile has a radius of curvature of 3.00m. If a bus is located at 5.00m from this mirror, find magnification?

  1. +0.23

  2. -0.23

  3. +0.45

  4. -0.45
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

$\dfrac{2}{R}=\dfrac{1}{u}+\dfrac{1}{v}$

$\dfrac{2}{3}=\dfrac{1}{-5}+\dfrac{1}{v}$
$\dfrac{1}{v}=0.866 \Rightarrow  v = 1.15$ cm
Magnification 
$=-\dfrac{v}{u}=-\dfrac{1.15}{-5}=0.23$

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

What is known as linear magnification of spherical mirrors?

  1. Ratio of size of image to size of object

  2. Ratio of shape of image to size of object

  3. Ratio of size of image to shape of object

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


Ratio of size of image to size of object is known as linear magnification of spherical mirrors.

Linear magnification (m) is the ratio of height of image to that of the object.

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

For magnification in spherical mirrors object height is :

  1. Negative.

  2. Positive.

  3. For real images positive.

  4. For virtual images negative.
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Magnification is the increase in the image size produced by spherical mirrors with respect to the object size. It is the ratio of the height of the image to the height of the object. The height of the object is always positive as the object is always above the principal axis. 

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

In case of a real and inverted image, the magnification of a mirror is:

  1. Positive

  2. Negative

  3. Zero

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

We know,
Magnification(M)$=\dfrac{height  \ of\   image({h} _{i})}{height\   of  \ object({h} _{o})}$
Here,image is inverted so the $height \  of \  image({h} _{i})$will be negative.
Hence, the magnification of a mirror is negative.