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

Where is the image of an object formed by a plane mirror?

  1. On the surface of mirror

  2. Just in the front of mirror

  3. Just behind the mirror

  4. At double the distance behind the mirror
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Yes, it is correct. The image is formed at the same distance behind the mirror as the object is in front of it.

Multiple choice maths complementary angle, supplementary angles and adjcent angles acute and obtuse angles types of angle measurement of an angle

Let the slope of the lines upon which the incident ray and line mirror lie are respectively $5$ and $3$, then the slope of the line upon which the reflected ray lies is 

  1. $1$
  2. $2$
  3. less than $2$
  4. more than $2$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

The law of reflection states that the angle of incidence equals the angle of reflection. Using the formula for the angle between lines with slopes m1 and m2, tan(theta) = |(m2-m1)/(1+m1m2)|. Setting the angle of the incident ray equal to the reflected ray relative to the mirror slope, the resulting slope is 1.

Multiple choice

Which of the following items does NOT reflect light?

  1. A mirror

  2. A white car

  3. A black shirt

  4. Aluminum foil
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

A black shirt absorbs most of the light that hits it rather than reflecting it. Mirrors, white surfaces, and shiny metals like aluminum foil are highly reflective.

Multiple choice evs magic with mirrors introduction to light and mirror image formation by plane mirror light : reflection and refraction from plane surface

In case of reflection by a plane mirror, which of the following statement are not correct?

  1. It can never give real image

  2. It can never give inverted image

  3. It changes left into right

  4. It changes front into back
Reveal answer Fill a bubble to check yourself
A,B,D Correct answer
Explanation

In case of reflection an by a plane mirror, it does not give a real, inverted image and image never changes front into back.

Multiple choice evs magic with mirrors introduction to light and mirror image formation by plane mirror light : reflection and refraction from plane surface

An object is placed symmetrically between the two plane mirrors inclined at angle of $30^o$. Then the total number of images formed is:

  1. 12

  2. 2

  3. 11

  4. 15
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

No. of image $ = \dfrac{ 360^{\circ}}{ \theta} – 1$

                                             $ = 12-1$
                                             $ = 11$

Multiple choice physics light : reflection and refraction from plane surface introduction to light and mirror magic with mirrors image formation by plane mirror principle of reversibility of path of light refractive index

A plane mirror is in a vertical plane and is rotating about a vertical axis at 100 mm horizontal beam of light is incident on the mirror. The reflected beam will rotate at

  1. $100 rpm$
  2. $141 rpm$
  3. $0 rpm$
  4. $200 rpm$
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

When a mirror rotates at an angular velocity omega, the reflected ray rotates at an angular velocity of 2*omega. Therefore, if the mirror rotates at 100 rpm, the reflected beam rotates at 200 rpm.

Multiple choice physics light : reflection and refraction from plane surface introduction to light and mirror magic with mirrors image formation by plane mirror principle of reversibility of path of light refractive index

When a mirror is rotated through an angle, the reflected ray moves through double that angle, the instrument based on the above principle is :

  1. Periscope

  2. Odometer

  3. Refractometer

  4. Sextant
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

A periscope is based on the principle of reflection.

An Odometer is used to measure the distance travelled by a vehicle.
A Refractometer is based on the principle of refraction (Snell'slaw).
A Sextant is used to measure the angle between two visible objects. Baesd on the principle that when a mirror is rotated through an angle the reflected ray moves through double of that angle.

Multiple choice physics light : reflection and refraction from plane surface introduction to light and mirror magic with mirrors image formation by plane mirror principle of reversibility of path of light refractive index

In a Michelson experiment for measuring speed of light, the distance traveled by light between two reflections from the rotating mirror is 4.8 km. The rotating mirror has a shape of a regular octagon. At what minimum angular speed of the mirror (other than zero) the image is formed at the position where a non-rotating mirror forms it?

  1. $780$ $rev/s$
  2. $7800$ $rev/s$
  3. $690$ $rev/s$
  4. $7500$ $rev/s$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Minimum angular speed $ f=\dfrac { c }{ dN }$


$ =\dfrac { 3\times { 10 }^{ 8 } }{ 4.8\times { 10 }^{ 3 }\times 8 }$

$ =7812rev/s\cong 7800rev/s$

Multiple choice physics light : reflection and refraction from plane surface introduction to light and mirror magic with mirrors image formation by plane mirror principle of reversibility of path of light refractive index

A plane mirror which rotates $10^4$ times per minute reflects light on to a stationary mirror $50$ m away. This mirror reflects the light normally so that it strikes the rotating mirror again. The image observed in the rotating mirror is shifted through $2.4$ minutes from the position it occupies. When the rotating mirror is stationary, what is the speed of light?

  1. $3\times 10^8$ m/s
  2. $4\times 10^8$ m/s
  3. $5\times 10^8$ m/s
  4. $6\times 10^8$ m/s
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

This is a classic Fizeau or Michelson-type experiment setup. Using the formula for the speed of light c = 4*N*D*theta, where N is frequency, D is distance, and theta is the deflection angle, the calculation yields 3*10^8 m/s.

Multiple choice physics light : reflection and refraction from plane surface introduction to light and mirror magic with mirrors image formation by plane mirror principle of reversibility of path of light refractive index

Light incident on a rotating mirror M is returned to a fixed mirror N placed 22.5 km away from M. The fixed mirror reflects it back to M (along the same path) which in turn reflects the light again along a direction that makes an angle of $\displaystyle { 27 }^{ o }$ with the incident direction. The speed of rotation of the mirror is: 

  1. 250 revolutions $\displaystyle { s }^{ -1 }$
  2. 500 revolutions $\displaystyle { s }^{ -1 }$
  3. 1000 revolutions $\displaystyle { s }^{ -1 }$
  4. 125 revolutions $\displaystyle { s }^{ -1 }$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation
Suppose the number of revolutions are n. The angle between 2 positions of the rotating mirror  = $\dfrac { 1 }{ 2 } \times 27\quad degrees$.

Since the angle of rotation of mirror is half the angle through which the reflected ray rotates.

The time taken by the mirror in rotating through an angle $\theta $ is given by $t=\dfrac { \theta  }{ 2\pi n } =\dfrac { 13.5\quad degrees }{ 2\times 180\times n } sec.$ -- Eqn 1

This is also the time taken by the light to travel from original point to the fixed mirror and back, thus

$t=\dfrac { 2d }{ c } =\dfrac { 2\times 22500 }{ 3\times { 10 }^{ 8 } } [d=22.5\quad km=22500m\quad and\quad c=3\times { 10 }^{ 8 }m/s]$ -- Eqn 2

From eqns 1 and 2,

$\dfrac { 13.5 }{ 2\times 180\times n } =\dfrac { 2\times 22500 }{ 3\times { 10 }^{ 8 } } $

or n = $\dfrac { 13.5\times 3\times { 10 }^{ 8 } }{ 2\times 180\times 2\times 22500 } =\dfrac { 40.5\times { 10 }^{ 8 } }{ 16200000 } =\dfrac { 40500\times { 10 }^{ 5 } }{ 162\times { 10 }^{ 5 } } =250\quad revolutions/s$.

Hence, the number of revolutions are 250 revolutions/s.