light

Question 1

what is electromagnetic wave

Answer 1

in which electric and magnetic field oscillates perpendicular to eachother and wave also propagates perpendicular to both the fields.

Question 2

what is the speed of light in vacuum and air

Answer 2

299.792,458m/s. 2.95 multiplied by 10^8m/s. due to negligible difference we take it as 3 multiplied by 10^8 m/s

Question 3

what does the nature of light depend upon

Answer 3

the dimension of particle. if light strikes an object whose dimension is equal to or less than the wave length of light then it will behave as particle.

Question 4

what is extended and point object

Answer 4

point object is the one which has negligible dimensions. extended object is the one which has considerable dimensions. only single ray comes from point object. and multiple rays come from extended object.

Question 5

what is a real object and real image

Answer 5

from real object rays are actually coming and in real image rays are actually meeting at a point.

Question 6

what is virtual image

Answer 6

in which rays are appearing to meet, it is not formed due to actual intersection of reflected light rays

Question 7

what is reflection of light? what is necessary for it?who is the best reflector?

Answer 7

bouncing back of light from a polished and smooth surface. into the same medium when it strikes a reflecting surface. for this, opacity of the surface is necessary. silver is the best reflector

Question 8

what is oblique incidence, normal incidence, and grazing incidence

Answer 8

angles is greater than 0 degree and less than 90 degree. angle is 0 degree. angle is 90 degree.

Question 9

what is regular and irregular reflection

Answer 9

rays are parallel before incidence and after reflection, and the normal is also parallel and angle of incidence will be the same for each ray. also known as specular reflection, it takes place on a smooth surface. irregular reflection is also known as diffused reflection. rays are parallel before incidence but nor parallel after reflection as normal aint parallel too. angle of incidence will be different for each ray. takes place on an irregular surface. irregular surface does not mean the failure of laws of reflection light

Question 10

what are the properties of image formed by a plane mirror

Answer 10

the image is virtual, erect, laterally inverted, image is formed at a same distance as that of object. same size as that of object, height of object= height of image.

Question 11

what is a spherical mirror

Answer 11

mirror with curved reflecting surface. spherical mirrors are a part of a sphere.

Question 12

define centre of curvature and radius of curvature

Answer 12

centre of a hollow sphere of which mirror is a part. incase of concave mirror it is infront of reflecting surface and incase of convex mirror it is behind the reflecting surface. It is the radius of the sphere of which mirror is a part. radius of curvature is inversely proportional to curvature.

Question 13

what is the curvature and radius of a plane mirror and pole

Answer 13

the curvature of a plane mirror is 0 and radius is infinity and pole can be any point on a plane mirror

Question 14

what is principal axis

Answer 14

imaginary line joining the pole at the centre of curvature

Question 15

what is pole

Answer 15

point at which principal axis is perpendicular to mirror or it is the centre point or the midpoint of spherical mirror

Question 16

what is aperture

Answer 16

it is the effective diameter[ which changes ] of spherical mirror . it is the part of the mirror available for reflection

Question 17

what is delta

Answer 17

it is the angle of deviation or the angle between reflected and undeviated incident ray[ extended incident ray]. delta= 180-2<i or 2<r. <i or <r = 180- delta divided by 2

Question 18

what is electromagnetic spectrum

Answer 18

it is the range of all types of EM radiation, organised by frequency or wavelength. radiation is energy that travels and spreads out as it goes. the visible light that comes in your house and the radio waves that come from a radio station are two types of electromagnetic spectrum

Question 19

what is visible spectrum or light

Answer 19

the visible spectrum is the band of the electromagnetic spectrum that is visible to the human eye. we can see these waves as the colors of the rainbow where each color includes a different wavelength. ROYGBIV[decreasing order of wavelength and increasing frequency]

Question 20

how can we find the energy of light

Answer 20

Elight=NHF where f is the frequency, h is plank’s constant[6.626 multiplied by 10^-34 J.S, n is equal to the number of photons

Question 21

what is the wavelength of light? relation between wavelength and velocity of light

Answer 21

approximately 400-700nm. f= c divided by lambda[wavelength].

Question 22

what is rectilinear propagation of light

Answer 22

light travels in a straight line until it strikes an obstacle.

Question 23

does ray of light exist

Answer 23

no, it does not exist practically it is only defined to understand rectilinear propagation of light[ it is only theoretical]

Question 24

does speed of light remain constant in a given medium?

Answer 24

speed of light remains constant in a given medium [conditions apply], but when it travels from one medium into another it’s speed changes

Question 25

when does the cross section area remain same, decrease and increase?

Answer 25

where there is a parallel beam of light[ bunch of rays] , diverging beam, converging beam the cross section area remains same, increases and decreases respectively

Question 26

what are photons

Answer 26

small energy pockets

Question 27

what is light? state some properties of light

Answer 27

light is a form of enrgy which enable us to see any object or gives us sensation of vision or sight. light is an electromagnetic wave as well as non mechanical[light does not need material medium that is it can travel in vacuum also] + transverse wave. it is not deviated by electric and magnetic field. light always follows that path from which it can travel faster or it can take less time, but that path may or may not be the shortest path for light. light has dual nature

Question 28

a ray which comes from infinity is

Answer 28

always parallel to principal axis

Question 29

normal always passes through

Answer 29

centre of curvature

Question 30

what is focus

Answer 30

it is always the mid point of spherical mirrors. It can be defined as the image point of that object which is at infinity or that point on principal axis which divides it into 2 equal parts.

Question 31

how many rays are needed for image formation

Answer 31

minimum 2 rays

Question 32

what is focal length and what is it equal to

Answer 32

it is the distance between pole and focus. F= R/2 and R= F/2

Question 33

what are the rules for image formation in case of concave mirror

Answer 33

a rays which is parallel to principal axis always passes through focus
rays which pass through focus become parallel to principal axis after reflection
a rays passing through center of curvature retraces its path.

Question 34

what are the rules for image formation in case of convex mirror

Answer 34

rays parallel to principal axis appear to diverge from focus in
a ray which is directed towards focus becomes parallel to principal axis after reflection
a ray which is directed towards centre of curvature retraces its path

Question 35

list some points of sign convention or cartesian

Answer 35

object should be placed towards left[reflecting surface] of mirror.
pole is the origin i.e., all distances are measured pole.
distance in the direction of incident ray is positive and direction opposite to incident ray are negative.
height above principal axis which is erect is taken as negative and height below principal axis which is inverted is taken as negative.

Question 36

symbol of object distance. is the distance taken as negative or positive. what is the height of the object taken as?

Answer 36

u. Negative always. Positive

Question 37

image formation rule in case of concave mirror when object is at infinity[principal axis ke bahar]

Answer 37

image is formed at focus.
image formed is real
image is point sized or highly diminished

Question 38

form a table of image formation

Answer 38

object image

infinity at f
beyond c between c and f
at c at c
between c and f beyond c
at f infinity

size

highly diminished[point sized]
diminished { all the images formed
are real and inverted
except the [point sized
image which is only
real}
same size
enlarged
highly enlarged

Question 39

image formation when object is between p and f

Answer 39

image behind mirror
image is virtual and erect
size is enlarged

Question 40

where does the incident ray passes from incase of concave mirror when object is beyond c

Answer 40

the incident ray passes from the focus or center of curvature

Question 41

in which case of concave mirror the image formed is virtual and erect

Answer 41

when object is between f and p

Question 42

radius of curvature is equal to

Answer 42

1/ curvature