Tag: physics

Questions Related to physics

Wave front means:

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

  1. all particles in it have same phase

  2. few particles are in same phase, rest are in opposite phase

  3. all particles have opposite phase of vibrations

  4. all particles have random vibrations

Show answer
Correct Option: A
Explanation:

All particles in it have same phase.

It is the imaginary surface representing corresponding points pf a wave that vibrate in unison. When identical waves having a common origin travel through a homogeneous medium , the corresponding crests and troughs at any instant phase.

A wavefront is an imaginary surface where :

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

  1. phase is same for all points

  2. phase changes at constant rate at all points along the surface

  3. constant phase difference continuously changes between the points

  4. phase changes all over the surface

Show answer
Correct Option: A
Explanation:

A wave front is the locus of points having the same phase.
Hence option A is correct.

The shape of wave front at a very large distance from source is ______

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

  1. Circular

  2. Spherical

  3. Cylindrical

  4. Plane

Show answer
Correct Option: D
Explanation:

Due to the large distance, the radius of the wavefront can be considered as large (infinity) and hence, a wavefront is almost plane.

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?

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

  1. $\cos ^ { - 2 } \frac { 2 } { \sqrt { 14 } }$

  2. $\cos ^ { - 1 } \frac { 2 } { \sqrt { 14 } }$

  3. $\cos ^ { - 3 } \frac { 2 } { \sqrt { 14 } }$

  4. $\cos ^ { - 4 } \frac { 2 } { \sqrt { 14 } }$

Show answer
Correct Option: B
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. 

Light waves travel in a vacuum, along the $X-$axis. Which of the following may represent the wave fronts?

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

  1. $x=c$

  2. $y=c$

  3. $z=c$

  4. $x+y+z=c$

Show answer
Correct Option: A
Explanation:

Given the direction of propagation is $ \hat{i} $
Wave fronts will be planes $ \perp \hat{i} $
In the given options, only plane $ x=c $ is  $ \perp \hat{i} $

The wavefront is a surface in which

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

  1. all points are in the same phase

  2. there is a pair of points in opposite phase

  3. there is a pair of points with phase difference $(\dfrac{\pi}{2})$

  4. there is no relation between the phases

Show answer
Correct Option: A
Explanation:

A wavefront is the locus of points characterized by propagation of position of the same phase: a propagation of a line in 1D, a curve in 2D or a surface for a wave in 3D.

The wave front is a surface in which:

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

  1. All points are in the same phase

  2. There is a pair of points in opposite phase

  3. There is a pair of points with phase difference $(\cfrac {\pi}{2})$

  4. There is no relation between the phase

Show answer
Correct Option: A
Explanation:

 A wavefront is the locus of points having the same phase.

In null method of comparison of magnetic moments, the net magnetic field at the centre of the DMM, when null deflection is obtained is

uniform magnetic field lines of earth magnetism physics

  1. $0$

  2. $B _{H}$

  3. between $0$ and $B _{H}$

  4. above $B _{H}$

Show answer
Correct Option: B
Explanation:

In null method , two magnets are kept on either side of the arms so that the net deflection is zero . So the magnetic field due to the bar magnets gets cancelled and only earth's horizontal magnetic field is left

In both $\tan A$ and $\tan B$ positions in a Deflection Magnetometer,  the bar magnet is always placed

uniform magnetic field lines of earth magnetism physics

  1. parallel to the magnetic needle of the deflection magnetometer

  2. parallel to the aluminum pointer of the deflection magnetometer

  3. perpendicular to the aluminum pointer

  4. parallel to the arm having the wooden scale

Show answer
Correct Option: A
Explanation:

In $\tan A$ position the bar magnet is placed horizontally, parallel to the arm of the deflection magnetometer and parallel to the magnetic needle of the deflection magnetometer. 

In $\tan B$ position the bar magnet is placed horizontally, perpendicular to the arm of the deflection magnetometer and parallel to the magnetic needle of the deflection magnetometer. 

The absolute value of earths magnetic horizontal intensity is determined with the help of

uniform magnetic field lines of earth magnetism physics

  1. DMM only

  2. VMM only

  3. DMM & VMM

  4. Plane mirror

Show answer
Correct Option: C
Explanation:

The absolute value of earths magnetic horizontal intensity is determined with the help of DMM and VMM.