Light

The field of view is maximum for b)convex mirror because it always forms virtual ,erect .small sized image of object. That is the reason we use convex mirror in our vehicles.

(A) This is incorrect because –

plane mirror always form equal size image of object ,this is the reason we not prefer plan mirror for large field of view.

(B) This is incorrect because-

Concave mirror has small field of view then convex mirror .

45 , if ray is travelling from lighter to denser medium then after refraction it bend towards the normal between the surfaces.

(a) If angle of incident is 0. Then the ray will go on its own path it will not show any deflection . so there is no refraction.

SEE the figure below to get an idea how ray will travel when angle of incident is zero.

So this option is incorrect

(c)As angle of incident is 90 , there is also no refraction.

Because when the bulb of torchlight is placed at focus of concave mirror, it allows the light to spread out to infinity (longer distances).

(b)this is incorrect because

convex mirror always forms virtual images so we can not put light bulb on virtual position so we can’t use convex mirror in torch light.

(c)this is incorrect because –

plane mirror can not spread light falling on it so we not use it in torch light.

 A virtual image formed by a concave mirror is always enlarged.

 When an object is placed between a concave mirror and its focal point, the image is virtual.

(b) This is incorrect because-

the convex mirror forms virtual images, but it is not enlarged.

(b) This is incorrect because-

Plane mirror always forms equal sized images.

(b)This incorrect because the concave mirror is curved inwards.

(c) this is incorrect because the plane mirror is plane.

Focal length of a mirror is given by the following formula.

f=R/2

Where R=radius of the mirror

So R=5× 2 = b)10 cm

(a)&(c) not have the value equal to 10cm so both are incorrect .

When the light ray passes through prism its is deviated and dispersed due to refraction of light.

Option (a)&(c) are incorrect

Only (b) is correct

vacuum , the refractive index in vacuum is 1.

(b)&(c) is incorrect because the refractive index in both cases is higher then 1.

(b)This is incorrect because the plane mirror always form equal sized image .

(a) This is incorrect because convex mirror always forms virtual images .

Because we know that Two important conditions for total internal reflection are:

• Angle of incidence (i) should be greater than critical angle (i_c).

• Ray should travel from denser medium to rarer medium.

There are three cases for a ray going from water to air ,these are

Clearly shown in the figure -

1) Normal refraction

2) Critical angle

3) Total internal reflection

As clearly shown in the above when the ray of light from air is going into glass it will deviated from its path .as we known glass is denser then air, so according to the laws of refraction when light is travels from less dense medium to more dense medium it will bend towards the normal , that is the reason the angle of refraction become less then the angle of incident .

So , angle of refraction (r) < angle of incident(i)

As we all know that

We also know that

Speed of light in a vacuum is = 3 × 10⁸ ms^-1

So,

Speed of light in diamond =1.244×10⁸m/s

TRUE

FALSE

It will show deviation due to the difference between the REFRACTIVE INDEX of two medium.

false

The image will form at principal focus , the image will be virtual and point sized.

FALSE

THE distance between the plane mirror and object will be same as the distance between plane mirror and image . The distance between object and image will be 6 cm.

TRUE

false , its called the radius of curvature

false

The image is at the centre of curvature itself. It is i) Real, ii) inverted and

iii) same size as the object.

false ,speed of light is fasted it is 3 × 10⁸ ms^-1

false , Critical angle has angle of incidence 90°.

True

In going from a rarer to denser medium, the ray of light bends _TOWARDS THE NORMAL

The ratio of sine of the angle of incidence to the sine of ANGLE OF REFRACTION is a constant.

The mirror used in search light is CONCAVE.

The angle of deviation of light ray in a prism depends on the angle of PRISM.

The radius of curvature of a concave mirror whose focal length is 5cm is 10cm.

A spherical mirror whose reflecting surface is curved outwards is called CONVEX mirror

Large CONCAVE mirrors are used to concentrate sunlight to produce heat in solar furnaces

All distances parallel to the principal axis are measured from the principal axis of the mirror

A negative sign in the value of magnification indicates that the image is REAL.

Light is refracted or bent while going from one medium to another because its REFRACTIVE INDEX changes.

C) Assertion is false because –

CONVEX MIRROR IS USED INSTEAD OF PLANE MIRROR

A)you can clearly see in the figure how ray will travel.

1) glass 2) water

According to Cartesian sign convention, object distances (u) are always negative as the object is placed to the left of the mirror/lens.

• Focal length (f) is positive for a convex lens and convex mirror.

• Focal length is negative for concave lens and concave mirror.
Image distance (v) can be both positive and negative for convex lens and concave mirror depending on the position of the object.

• Image distance is always negative for a concave lens.

• Image distance is always positive for a convex mirror.

It happens due to the, phenomenon of refraction of light. When the rays of light from the coin, in the denser medium which is water, fall on the interface separating the two media, the rays of light move away from the normal after refraction. The point from which the refracted rays appear to come gives the apparent position of the coin. As the rays appear to come from a point above the coin, therefore, the coin appears some distance above the base of beaker.

(i) Concave mirror gives an erect and enlarged image of an object, when the object is between pole (P) and principal focus of mirror (F).

(ii) Concave mirror gives same sized and inverted image when object is place on centre of curvature of the mirror.

1) convex mirror

2) Concave mirror

If an object is placed at the focus of a concave mirror,then a large image appears at infinity . after reflection the rays meet at infinity .

the ray will become pallarel to the principal axis.

when a light ray travels from one medium to another, it shows some deviation from its path this phenomenon is called refraction of light.

the speed of light in vaccum is 3 × 10⁸ ms^-1

It was the Danish astronomer, Olaus Roemer, who, in 1676, first successfully measured the speed of light. His method was based on observations of the eclipses of the moons of Jupiter (by Jupiter)

Concave mirror produces virtual, erect and magnified images when a object is placed in between focus and pole. That’s the reason why dentists use concave mirror to examne teeth.

(a)

(b) When the object AB is placed between the centre of curvature and principal focus, then the ray AD going parallel to the principal axis and another ray AE passing through the principal focus F intersect each other at point A’ beyond the centre of curvature. Thus the image formed in this case is beyond C, enlarged, real and inverted.

concave mirror - Dentist’s mirror, Torch-light mirror , Make-up mirror.

Convex mirror - Rear-view mirror , Mirrors in shopping malls

A ray of light passing through the centre of curvature of a concave mirror retraces its path (gets reflected along the same path), because as the ray of light passes through centre of curvature of a concave mirror it strikes the mirror along the normal and it incidences on to the mirror at 90 degree. Hence the incident ray coincides with the normal.

Therefore angle of incidence = 0 .As we know according to law of reflection angle of reflection = 0, hence the angle of reflection too become zero degree, thus ray of light retraces its path.

Magnification – magnification is defined as how many times bigger or smaller the image of the object formed by the spherical mirror.

It is defined as the ratio of the height of the image to the height of the object.

Let , height of the object = h_o

Height of the image =h_i

Then the magnification

Magnification can also be defined as ratio of object distance(u) and the image distance (v)

The sign will be

• negative for real image

• positive for virtual image

The spherical mirror formula is the relation among the image distance ,object distance and focal length of the mirror .

If The image distance is = v

The object distance is = u

The focal length of mirror =f

Then the mirror formula will be –

The sign convention can be used as given in the figure –

We can see following things from the figure –

• Focal length (f) is positive for a convex lens and convex mirror.

• Focal length(f) is negative for concave lens and concave mirror.

• Image distance (v) can be both positive and negative for convex lens and concave mirror depending on the position of the object.

• Image distance(v) is always negative for a concave lens.

• Image distance(v) is always positive for a convex mirror.

• Object distance (u) is negative for convex as well as the concave mirror.

(a)

• Image is inverted and same size

(b)

• Image is inverted , real and large in size

(c)

• Image will be Virtual and large in size

Refraction of light take place when light travels between two medium. As the speed of light is different in different medium that is the major factor for refraction of light .

(a)

As you can see in this figure the light is travelling from less dense medium to more dense medium ,its path is deviated ,this is because of refraction taking place between these two medium.

Whenever the light travels from less dense medium to more dense medium it will bend towards the normal to the surface.

As you can see in the diagram incident ray bends towards the normal axis .

In this case always incident angle I > r (angle of refraction)

(b)

when the ray of light travels from more dense medium to less dense medium it move away from the normal axis. As you can see in the following figure

Consider the figure above when light ray passes through the interface of two medium it will deviated from its path . in this case always

Angle of incident I < r (angle of refraction)

(c) when the light ray incident normally to the interface of two medium then it travels in same path , no deviation will be there. Because the angle of incident will be 0.

You can see this in following figure –

There are two Laws of Refraction these are –

• The incident ray, the refracted ray and the normal to the surface at the point of incidence all lie in one plane.

• For any two given pair of media, the ratio of the sine of the angle of incidence to the sine of the angle of refraction is a constant.

• The second law is called Snells Law after the scientist Willebrod Van Roijen Snell who first formulated it.
Thus, Sin i by Sin r (where the i is the angle of incident and r is the angle of refraction) is equal to a constant that is equal to μ where, mew is the refractive index of the second medium (R2) with respect to the first medium (R1).

Hence

There are the procedure how we can verify the laws of refraction-

• Place a rectangular glass slab on a white sheet of paper fixed to a drawing board.

• Trace the boundary A1B1C1D1 of the glass slab.

• Remove the glass slab.

• Draw IO to represent the incident ray.

• Draw the normal MN at the point of incidence O.

• Fix two pins P1 and Q1 on the incident ray IO.

• Place the glass slab within its boundary A1B1C1D1.

• Look in from the other side of the glass slab, fix two pins R1 and S1 such that the feet of all the pins are in one straight line.

• Remove the glass slab and the pins.

• Mark the pin points P1, Q1, R1 and S1.

• Join R1 S1 to represent the emergent ray O2 E.

• Join O1O2 . O1O2 dash is the refracted ray.

The incident ray, the refracted ray and the normal are all lying in the same plane. This proves the first law of refraction.

Measure and record the angle of incidence(i) and angle of refraction(r).
Repeat the experiment by varying the angle of incidence and Measure the corresponding angle of refraction.
Now find the ratio of the sine of the angle of incidence(i) to the sine of the angle of refraction(r).

The ratio of the sine of the angle of incidence to the sine of the angle of refraction is found to be the same in all the three cases.

This verifies the second law of refraction or Snells law that is sin i by sin r is equal to μ , a constant for a given pair of media.

When an object is placed between the principal focus (F) of the mirror and the pole of the mirror (P) then the image of the object is become on the back side of the mirror ,

YOU can see the image formation in above figure ,where the object AB is placed between focus and pole of the mirror and the image of the object AB is formed other side of the mirror .

This image will be –

• Virtual

• Large then the image

• And erect.

as we know focal length f = R/2

Given that radius of curvature R = 40cm

Then the focal length will be

f = R/2 =40/2 = 20cm.

given that

Object height h_o = 2 cm

Object distance u = -20cm (left side of mirror)

Focal length f = -12cm (concave mirror)

As we know mirror equation -

V= -30

As we know magnification is

Putting values in formula we get -

h_i=3cm

Thus the image is 30cm from pole of mirror , its height will be 3 cm ,its real, inverted and magnified

Given that-

Object distance u = -7cm (left side of mirror)

Magnification m = 3

Image is real then the magnification formula become –

Putting values in formula we get -

V = 21cm

The image is located at 21 cm in front of mirror

Given that –

Refractive index of glass =1.5

Speed of light in vacuum = 3 × 10⁸ ms^-1

As we know

So

Speed of light in glass =2×10⁸m/s

Given that –

Speed of light in water is = 2.25 × 10⁸ ms^-1

Speed of light in vacuum = 3 × 10⁸ ms^-1

As we know

So

The refractive index of water =1.33