Physics

Optics and Lenses

206 Questions

Enhance your physics knowledge by practicing questions on optics and the functioning of lenses. The set covers calculating combined focal lengths, lens power, and correcting vision defects like myopia and hypermetropia. These physics fundamentals are crucial for medical entrance and state board exams.

Combined focal lengthCorrecting vision defectsLens power calculationConvex and concave lensesTelescopesHuygens principle

Optics and Lenses Questions

Multiple choice evs light and shadow dual nature of light nature and sources of light theories on light

Which of the following is incorrect?

  1. A thin convex lens of focal length ${f} _{1}$ is placed in contact with a thin concave lens of focal length ${f} _{2}$. The combination will act as convex lens if ${f} _{1}<{f} _{2}$
  2. Light on reflection at water-glass boundary will undergo a phase change of $\pi$

  3. Spherical aberration is minimized by achromatic lens

  4. If the image of distant object is formed in front of the retina then defect of vision may be myopia
Reveal answer Fill a bubble to check yourself
B Correct answer
Multiple choice evs light and shadow dual nature of light nature and sources of light theories on light

The inability of a lens to bring all the rays coming from a point object to focus at one single point is called

  1. Spherical aberration

  2. Parallex

  3. Optical illusion

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

Spherical aberration occurs when a lens cannot focus all rays from a point source to a single point due to the spherical shape of the lens surfaces.

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 radii of curvature of the surfaces of a double convex lens are 20 cm and 40 cm respectively, and its focal length is 20 cm. What is the refractive index of the material of the lens.? 

  1. $\dfrac{5}{2}$
  2. $\dfrac{4}{3}$
  3. $\dfrac{5}{3}$
  4. $\dfrac{4}{5}$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Here $R _1$ = 20 cm, $R _2$ = -40 cm, f = 20 cm
Using lens maker's formula we get,
$\dfrac{1}{20} \, = \, (\mu \, - \, 1) \left ( \dfrac{1}{20} \, + \, \dfrac{1}{40} \right )$
$\dfrac{1}{20} \, = \, (\mu \, - \, 1) \dfrac{3}{40} \, \Rightarrow \, \mu \, = \, \dfrac{5}{3}$

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

Radius of curvature is found to be equal to twice the focal length for:

  1. Plane mirror of small aperture

  2. Spherical mirrors of small aperture

  3. Plane mirrors of large aperture

  4. Spherical mirrors of large aperture
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

For spherical mirrors of small apertures, the radius of curvature is found to be equal to twice the focal length. We put this as $R = 2f$. This implies that the principal focus of a spherical mirror lies midway between the pole and centre of curvature.

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

A dobleconves lens of focal length $6 cm$ is made of glass of refractive index $1.5$ the radius of curvature of of one surface is double that of other surface. The value of small radius of curvature is

  1. $6 cm$
  2. $4.5 cm$
  3. $9 cm$
  4. $4 cm$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Lens maker's formula: 1/f = (n-1)(1/R1 - 1/R2). Given f=6, n=1.5, R1=x, R2=-2x (double-convex). 1/6 = (0.5)(1/x + 1/2x) = 0.5(3/2x) = 3/4x. So 4x = 18, x = 4.5 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

A converging bundle of light rays in the shape of cone with a vertex angle of 45 falls on a circular diaphragm of 20 cm diameter. A lens with power 5 D is fixed in the diaphragm. Diameter of face of lens is equal to that of diaphragm. If the vertex angle of new cone is 

  1. $
    \cfrac { 3 d } { 4 }
    $
  2. $
    \cfrac { 5 d } { 4 }
    $
  3. $
    2 d
    $
  4. $
    \cfrac { 3 } { 2 } d
    $
Reveal answer Fill a bubble to check yourself
B Correct answer
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 sign convention for mirrors sign convention for spherical mirrors sign convention for the measurement of distances

A convex lens is used to form an image of an object on a screen. If the upper half of the lens is blackened so that it becomes opaque, then

  1. Only half of the image will be visible

  2. The image position shifts towards the lens

  3. The image position shifts away from the lens

  4. The brightness of the image reduces
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

To form a image only two rays are needed .The total amount of light released by the object is not allowed to pass through the lens, intensity of image will decrease

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 focal length of a convex lens of refractive index $1.5$ is $f$ when it is places in air. When it is immersed in a liquid it behaves as a converging lens its focal length becomes $xf(x>1)$. The refractive index of the liquid

  1. $>3/2$
  2. $<(3/2)$ and $>1$
  3. $<3/2$

  4. all of these
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

$\dfrac { 1 }{ f } =\left( n-1 \right) \left( \dfrac { 1 }{ { R } _{ 1 } } +\dfrac { 1 }{ { R } _{ 2 } }  \right) $
$\Rightarrow \dfrac { 1 }{ f } =\left( \dfrac { 1.5 }{ 1 } -1 \right) \left( \dfrac { 1 }{ { R } _{ 1 } } +\dfrac { 1 }{ { R } _{ 2 } }  \right)$ when the lens is placed in air and 
$\dfrac { 1 }{ xf } =\left( \dfrac { 1.5 }{ y } -1 \right) \left( \dfrac { 1 }{ { R } _{ 1 } } +\dfrac { 1 }{ { R } _{ 2 } }  \right)$ when the lens is places in the liquid.
where $y=R.l.$ of the liquid
solving we get, $y=\dfrac {3}{2+1/x}$
Hence $(B)$ is correct.

Multiple choice physics wave optics huygens wave theory and wavefront wave propagation (huygens' construction) theories on light wave behaviour

Huygens principle of secondary waves

  1. allow us to find the focal length of a thick convex lens.

  2. give us the magnifying power of the microscope.

  3. is a geometrical method to find, the position of a wave front.

  4. is used to determine the velocity of light.
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Huygens's Principle states that every point on a wavefront is a source of secondary wavelets, which spread forward at the same speed.

Thus is enables to find the position of wavefront.

Multiple choice physics wave optics huygens wave theory and wavefront wave propagation (huygens' construction) theories on light wave behaviour

Huygen's concept of secondary wave

  1. allow up to find the focal length of a thick lens

  2. is a geometrical method to find a wavefront

  3. is used to determine the velocity of light

  4. is used to explain polarization
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Huygen proposed a hypothesis for the geometrical construction of the position of a common wavefront at any instant during the propagations of waves in a medium.