Tag: light, shadows and images

Quizzes (6) Questions (62)

Questions Related to light, shadows and images

Multiple choice evs light, shadows and images what makes things visible nature and sources of light light travels in straight line

Which of the following statements is true?

  1. The image formed by a pinhole camera is inverted because light travels in a straight line.

  2. Light does not change its direction on reflection.

  3. As we move the object away from the light source, the shadow of the object becomes smaller.

  4. Reflection is possible only from polished surface.
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Light changes its direction after reflection. As we move the object away from the light source, the shadow becomes larger as the distance between object and the light source increases. Reflection is possible from rough surface also.

Multiple choice evs light, shadows and images what makes things visible nature and sources of light light travels in straight line

Ray optics is valid when characteristic dimension are  

  1. much smaller than wavelength of light.

  2. of same order as wavelength of light

  3. much larger than wavelength of light

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

Ray optics is valid when characteristic dimension are much larger than wavelength of light . The size of obstacle must be much larger than the wavelength of light. If wavelength is comparable to the size of object, then diffraction could happen, but it cannot be explained using ray optics, it will require wave theory of light. 

Multiple choice evs light, shadows and images what makes things visible nature and sources of light light travels in straight line

The difference in speeds of a ray of light in glass and water is $2.5 \times 10^7 \,m/s$. If the $R.I$ of glass and water are $\dfrac{3}{2}$ and $\dfrac{4}{3}$ respectively, then the velocity of light in air is

  1. $2 \times 10^8 \,m/s$
  2. $2.25 \times 10^8 \,m/s$
  3. $3 \times 10^8 \,m/s$
  4. $2.5 \times 10^8 \,m/s$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Let c be the speed of light in air (vacuum). The speed in glass is c / (3/2) = 2c/3, and in water is c / (4/3) = 3c/4. The difference is given as 3c/4 - 2c/3 = c/12 = 2.5 x 10^7 m/s. Solving for c gives c = 12 * 2.5 x 10^7 = 3 x 10^8 m/s.

Multiple choice evs light, shadows and images what makes things visible nature and sources of light light travels in straight line

Light travels through a glass plate of thickness t and refractive index $\mu $ If c is the speed of light in vacuum, the time taken by light to travel this thicknes of glass is 

  1. $\mu tc$
  2. $\dfrac { tc }{ \mu } $
  3. $\dfrac { t }{ \mu c } $
  4. $\dfrac { \mu t }{ c } $
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

The speed of light inside the glass plate of refractive index mu is v = c/mu. The time taken to travel thickness t is distance divided by speed, which is t / (c/mu) = mu*t / c.

Multiple choice evs light, shadows and images what makes things visible nature and sources of light light travels in straight line

It is necessary to illuminate the bottom of a well by reflected solar beam when the light is incident at an angle $40^o$ to the vertical. At what angle to the horizontal should a plane mirror be placed?

  1. $65^o$
  2. $70^o$
  3. $75^o$
  4. $80^o$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

$\begin{array}{l} i+r=i+i=140 \ or\, \, i={ 70^{ 0 } } \end{array}$

Thus, plane mirror makes an angle of $20^0$ with  vertical and $70^0$  with horizontal.
Therefore  , the correct answer is option $C$.

Multiple choice evs light, shadows and images what makes things visible nature and sources of light light travels in straight line

The illumination on the screen, in case of a movie hall if the distance between the projector and the screen is increased by $1\%$ will be:

  1. increased by $1\%$
  2. decreased by $1\%$
  3. increased by $2\%$
  4. decreased by $2\%$
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Projector act as a point source

Hence   $E\propto \dfrac{1}{r^{2}}$
$\dfrac{dE}{E}=2\left(\dfrac{\Delta r}{r}\right)=2\times 1\%=2\%$
As the distance increases, the illumination will decrease.

Multiple choice evs light, shadows and images what makes things visible nature and sources of light light travels in straight line

Pick the only wrong statement in the following :

  1. Light travels with a speed greater than that of sound

  2. Light cannot travel through vacuum

  3. Light travels in a straight line

  4. Light is a wave motion
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Light travels through vacuum for sure as it does not need a material medium for its propagation. Sunlight is the biggest example for this.

Moreover, light has maximum speed in vacuum ,that is, $3\times 10^8$.