Physics · Science General

Optics and Light Properties

2,019 Questions

Optics and light properties focus on the behavior of light, including reflection, refraction, dispersion, and polarization. This topic also covers the wave nature of light, illumination, and the functioning of optical instruments like microscopes. Questions on these concepts are common in general science sections of SSC, Railways, and State exams.

Reflection and mirrorsRefraction and mediumsLight wave theoriesPolarization and intensity

Optics and Light Properties Questions

Multiple choice luminous intensity measurements physics

The one parameter that determines the brightness of a light source sensed by an eye is

  1. energy of light entering the eye per second

  2. wavelength of the light

  3. total radiant flux entering the eye

  4. total luminous flux entering the eye
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation
Luminous flux measures the perceived power of light by adjusting the varying sensitivity to various frequencies of the human eye.

Radiant flux measures the total power of the electromagnetic radiation and does not account for eye sensitivity.

Similarly energy of light entering does not account for the fact that wavelengths beyond visible range does not contribute to brightness.

Wavelength of light alone does not give any idea about the brightness of light either.

Answer. D) total luminous flux entering the eye.
Multiple choice luminous intensity measurements physics

Light from a point source falls on a screen.if the separation between the source and the screen is increased by $1\%$ the illuminance will decrease (nearly) by

  1. $0.5\%$
  2. $1 \%$
  3. $2\%$
  4. $4\%$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Illuminance depends on inverse of area and area is proportional to $r^{2}$ where is r is distance from the source to the point .
$illuminance \propto \dfrac{1}{r^{2}}$ 
$\dfrac{\partial (illuminance)}{\partial x}= -\dfrac{2\delta r}{r}$
hence changing distance by $1$% the illuminance will differ by $-\dfrac{2\delta r\times100}{r}= -2%$%
i.e,illuminance will decrease by $2$% 
option $C$ is correct

Multiple choice luminous intensity measurements physics

The brightness producing capacity of a source

  1. does not depend on its power

  2. does not depend on the wavelength emitted

  3. depends on its power

  4. depends on the wavelength emitted.
Reveal answer Fill a bubble to check yourself
C,D Correct answer
Explanation

The brightness producing capacity of a source "depends on its power" and "depends on the wavelength emitted" .
option $C,D$ are correct 

Multiple choice luminous intensity measurements physics

In, the visible region of the spectrum the rotation of the plane of polarization is given by $\displaystyle\theta=a+\frac{b}{\lambda^2}$. The optical rotation produced by a particular material is found to be $30^0$ per $mm$ at $\lambda=5000A^o$ and $50^0$ per $mm$ at $\lambda=4000A^o$.  the value of constant $b$ in degree $\mathring A^2$ per mm, will be

  1. $\displaystyle \frac{8}{9}\times 10^9$
  2. $\displaystyle -\frac{8}{9}\times 10^9$
  3. $\displaystyle \frac{9}{8}\times 10^8$
  4. $\displaystyle -\frac{9}{8}\times 10^8$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Given theta = a + b/lambda^2. For lambda1 = 5000 A, theta1 = 30. For lambda2 = 4000 A, theta2 = 50. Two equations: 30 = a + b/(5000^2) and 50 = a + b/(4000^2). Subtracting: 20 = b * (1/16*10^6 - 1/25*10^6) = b * (9 / 400*10^6). b = 20 * 400*10^6 / 9 = 8000/9 * 10^6 = 8/9 * 10^9.

Multiple choice luminous intensity measurements physics

An electric bulb is hanging over a table at a height of 1m above it.The illuminance on the table directly below the bulb is 40 lux. the illuminance at a point on the table 1 m away from the first point will be about

  1. 10.5 lux

  2. 14.1 lux

  3. 20.8lux

  4. 28.8 lux
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Let $ I $ be the intensity of bulb then

case I:$\ 40=\dfrac { I }{ 1\times 1 } \Rightarrow I=40cd$
case II: $ E=\dfrac { 40 }{ { \left( { 1 }^{ 2 }+{ 1 }^{ 2 } \right)  }^{ 3/2 } } =\dfrac { 40 }{ \sqrt { 8 }  } =14.1 lux$

Multiple choice luminous intensity measurements physics

As the wavelength is increased from violet to red, the luminosity

  1. continuously increases

  2. continuously decreases

  3. increases, then decreases

  4. decreases ,then increases
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

With increase in wavelength of visible light, the sensitivity to eye increases, reaches a peak at 555 nm and then decreases. So luminosity increases then decreases.


Answer. C) Increases, then decreases

Multiple choice luminous intensity measurements physics

The brightness of a source based upon sensation of eye is determine by:

  1. radiant flux entering the eye

  2. luminous flux entering the eye

  3. wavelength of light

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

Only light of visible range excites the retina of eyes. The range Light, which can human eyes sense is called Luminus of light.
Hence, (b) is correct.

Multiple choice luminous intensity measurements physics

A surface is receiving light normally from a source, which is at a distance of $8\ m$ from it. If the source is moved closer towards the surface, so that the distance between them becomes $4\ m$, then the angle through which the surface may be turned so that illuminance remain as it was: 

  1. $\theta=\cos^{-1}(1/3)$
  2. $\theta=\cos^{-1}(1/4)$
  3. $\theta=\cos^{-1}(1/8)$
  4. $\theta=\cos^{-1}(1/6)$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Illuminance E = (I / d^2) * cos(theta). Initially, E = I / 8^2 = I / 64. Finally, E = (I / 4^2) * cos(theta) = (I / 16) * cos(theta). Equating them: I / 64 = I / 16 * cos(theta) => cos(theta) = 16 / 64 = 1/4. Thus, theta = cos^-1(1/4).

Multiple choice luminous intensity measurements physics

An electric bulb is suspended at a vertical height $2\ m$ from the centre of a square table of side $2\ m$. If the luminous intensity of bulb is $60\ cd$ (candela), then the illumination at one corner of the table is:

  1. $8.16\ cd/m^{2}$
  2. $6.24\ cd/m^{2}$
  3. $9.25\ cd/m^{2}$
  4. $8.72\ cd/m^{2}$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Distance from bulb to corner r = sqrt(2^2 + 1^2 + 1^2) = sqrt(6). Cos(theta) = height / r = 2 / sqrt(6). Illuminance E = (I / r^2) * cos(theta) = (60 / 6) * (2 / sqrt(6)) = 10 * 2 / 2.449 = 20 / 2.449 = 8.16 cd/m^2.

Multiple choice luminous intensity measurements physics

Light from a source is analysed by an analyser. When the analyser is rotated, the intensity of the emergent light.

  1. Does not vary

  2. Remains uniformly dark

  3. Varies between maximum and zero

  4. Varies between maximum and minimum
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Let the intensity of the unpolarised light be $I _o$.
An analyser is used to polarized the light in one direction.
Intensity of light after passing through the analyser  $I' = \dfrac{I _o}{2}$
Intensity of light after passing through analyser remains constant $I _o/2$ even if the analyser is rotated by some angle.

Multiple choice luminous intensity measurements physics

 If light falls on the surface at an angle of $60^{0}$, then illuminance will be____

  1. $12$ lux
  2. $6$ lux
  3. $3$ lux
  4. $1.5$ lux
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Illuminance ($E$)  is  measured  in  lux.  The  lux  is  an  SI  unit 

used  when  characterizing illumination conditions of a surface:
$E = \frac {I}{R^2}  cos \alpha     lux$
where $I$ is the luminous intensity, $R$ is the distance and $\alpha$ is the surface angle.
Given $I = 300 cd$, $R = 10 m$, $\alpha = 60^o$
$\implies E = \frac {300}{10^2}    cos  60^o= 1.5   lux$

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

The wavefront of a light beam is given by the equation $x + 2 y + 3 z = c$ , (where c is arbitrary constant) then what is the angle made by the direction of light with the y-axis?

  1. $\cos ^ { - 2 } \frac { 2 } { \sqrt { 14 } }$
  2. $\cos ^ { - 1 } \frac { 2 } { \sqrt { 14 } }$
  3. $\cos ^ { - 3 } \frac { 2 } { \sqrt { 14 } }$
  4. $\cos ^ { - 4 } \frac { 2 } { \sqrt { 14 } }$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

The wave front equations must be of form $ax+by+cz=1$ where ${a^2} + {b^2} + {c^2} = 1$ 

$($ $a,b,c$ are cosines of angles made with $x,yx,z$ axes respectively $)$
applying this to the given equation$:$
${1^2} + {2^2} + {3^2} = {c^2}$
${c^2} = 14$
$c = \sqrt {14} $
${\cos ^{ - 1}}\dfrac{2}{{\sqrt {14} }}$
angle made with $y-$ axis is ${\cos ^{ - 1}}\dfrac{2}{{\sqrt {14} }}$
Hence,
option $(B)$ is correct answer. 

Multiple choice physics energy production scattering of light and its applications some natural phenomena of light effects of light

A beam of monochromatic light first travels through glass of R.I. $1.5$ and then through water (R.I. $=\dfrac{4}{3}$). If the difference in their wavelengths in the two media is $40$nm, then the wavelength of the monochromatic light in vacuum will be?

  1. $4000\overset{o}{A}$
  2. $4400\overset{o}{A}$
  3. $4800\overset{o}{A}$
  4. $5200\overset{o}{A}$
Reveal answer Fill a bubble to check yourself
B Correct answer
Multiple choice physics human eye and colourful world scattering of light and its applications some natural phenomena of light effects of light

One can not see through fog because:

  1. fog absorbed light

  2. light is scattered by the droplets in fog

  3. light surfers total reflection by the droplets in the fog

  4. the refractive index of fog is in infinity
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

We can not see clearly through fog because the light is scattered by the droplets in the fog. The light is scattered by very small particles, this phenomenon is called Tyndall effect.

Hence the option B is the right answer