Tag: physics

Questions Related to physics

A small plane mirror kept at the centre of a sphere of diameter $3\ m$, makes $12$ revolution per second. A thin light beam is made incident on the mirror. The linear speed of the light spot on the sphere, formed after reflection from the mirror is :

physics light and shadow formation of image by a pinhole camera pinhole camera shadow

  1. $18\pi\ m/s$

  2. $36\pi\ m/s$

  3. $72\pi\ m/s$

  4. $144\pi\ m/s$

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Correct Option: D
Explanation:

When plane mirror rotates through an angle $\theta$ , the reflected ray rotates through an angle 2$\theta$. So spot on the screen will make 2 x 12 = 24  revolution per second.

 
To find the velocity 
v=2$\pi$R x frequency 
=2$\pi$ x 3 x 24
=144$\pi$ m/s

 D is the Correct answer.
 

Intensity of light due to a point source at a distance $2m$ is $20$ units. The intensity due to the same source at a distance of $4m$ is

physics light and shadow formation of image by a pinhole camera pinhole camera shadow

  1. $2.5\ units$

  2. $6\ units$

  3. $80\ units$

  4. $5\ units$

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Correct Option: D

Light has a wave nature,because-

physics light and shadow formation of image by a pinhole camera pinhole camera shadow

  1. The light travel in a straight line

  2. Light exhibits phenomenon of reflection and refraction

  3. Lights phenomeno interference

  4. Light exhibits phenomeno of photo electric effect

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Correct Option: C

Which one statement is correct -

physics light and shadow formation of image by a pinhole camera pinhole camera shadow

  1. Speed of light in free space $= \frac{1}{\sqrt{\mu _0 \varepsilon _0}}$

  2. Speed of light in any medium $=\frac{1}{\sqrt{\mu \varepsilon}}$

  3. $\frac{E _0}{B _0}=2C$

  4. $\frac{B _0}{E _0}=4C$

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Correct Option: A

Light falls on a plane reflecting surface. For what angle of incidence is the reflected ray normal to the incident ray. 

physics light and shadow formation of image by a pinhole camera pinhole camera shadow

  1. $60^o$

  2. $45^o$

  3. $90^o$

  4. $30^o$

Show answer
Correct Option: D
Explanation:

The incident ray will have an angle of reflection of ${30^0}$ $($made with a surface normal to the mirror surface$).$

Hence,
option $(D)$ is correct answer.

Choose the correct option from the following 

$ Statement I:$ If the size of the hole in a pinhole camera is as big as the size of a green gram then the image becomes thick and the details of the image are not clearly seen. 

$Statement II:$ If the distance of the object from pinhole camera is increased then the size of the image that is observed on the screen also increases.

$Statement III :$ If the distance between screen and hole in the pinhole camera is increasing we observe the image is becoming blurred 

physics light, shadows and images formation of image by a pinhole camera pinhole camera shadow

  1. All are correct

  2. $I, II$ are correct

  3. $II, III$ are correct

  4. $I, III $are correct

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Correct Option: A

The speed of light in air is ___________ m/s.

physics light and shadow formation of image by a pinhole camera pinhole camera shadow

  1. $3$

  2. $3\times { 10 }^{ -5 }$

  3. $3\times { 10 }^{ 8 }$

  4. $3\times { 10 }^{ 10 }$

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Correct Option: C

The Image formed in a pinhole camera  is real. 

physics light, shadows and images formation of image by a pinhole camera pinhole camera shadow

  1. True

  2. False

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Correct Option: A

State the effect on the image formed by a pinhole camera if the size of the hole is increased.

physics light, shadows and images formation of image by a pinhole camera pinhole camera shadow

  1. The image becomes blurred

  2. The image gets sharper

  3. The image completely vanishes

  4. No image is formed to begin with

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Correct Option: A
Explanation:

If the size of the hole increases the image will be blurred as several 
images are formed which overlap each other

Motion of molecule in a substance is concluded by

particles of a gas ideal gases physics

  1. Using microscopes

  2. Mathematical postulates

  3. Using assumptions

  4. Observations from experiments

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Correct Option: D
Explanation:

Molecules are too small to be seen by microscope. Motion of molecules can be concluded by observations seen in experiment,such as diffusion of ink particles in water,light scattering experiments etc.