Tag: nature and sources of light

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Questions Related to nature and sources of light

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

How are non luminous objects visible to eye ?

  1. Non-luminous objects give away light

  2. Non-luminous objects reflect the light falling on them

  3. Non-luminous objects disperse the light falling on them

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

Non-luminous objects reflect the light falling on them and the reflected light are sensed by the eye and thus we are able to see non-luminous objects.

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

Read the given statements and select the correct option.
Statement 1 : Rahul placed a coloured plastic bottle in front of the beam of a torch light. Then he placed a transparent sheet of same size on the other side of bottle. No shadow will form on the screen.
Statement 2 : Translucent objects allow light to pass through them partially.

  1. Both statements 1 and 2 are true and statement 2 is the correct explanation of statement 1.

  2. Both statements 1 and 2 are true but statement 2 is not the correct explanation of statement 1.

  3. Statement 1 is true but statement 2 is false.

  4. Statement 1 is false but statement 2 is true.
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

A coloured plastic bottle is an opaque material. When a light beam is incident on it, a shadow will form on the screen. Light can easily pass through the transparent material.

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 $C$.