The laws of refraction of light : The incident ray, the refracted ray and the normal to the interface of two transparent media at the point of incidence, all lie in the same plane. The ratio of the sine of the angle of incidence to the sine of the angle of refraction is a constant for a light of given colour and for the given pair of media. This law is also known as Snell's law of refraction.
 If i is the angle of incidence and r is the angle of refraction, then
\(\frac { \sin { i } }{ \sin { r } } =constant\)
Verification of laws of refraction :

(1) Fix a sheet of white paper on a drawing board using drawing pins.
(2) Place a rectangular glass slab over the sheet in the middle. Draw the outline of the slab with a pencil. Let us name the outline as ABCD. Take four identical pins.
(3) Fix two pins. Say E and F, vertically such that the line joining the pins is inclined to the edge AB.
(4) Look for the images of the pins E and F through the opposite edge. Fix two other pins, say G and H, such that these pins and the images of E and F lie on a straight line.
(5) Remove the pins and the slab.
(6) Join the prints of the pins E and F and let it meet AB at O. Let EF meet AB at O. Similarly, join the prints of the pins G and H and Let it meet HG at O'. Join o and O'. Also produce EF as shown by a dotted line in Figure.
(7) Draw a perpendicular NN' to AB at O and another perpendicular MM' to CD at O'. In this activity, you will note that, the light ray has changed its direction at points O and O'. Note that both the points O and O' lie on surfaces separating two transparent media. The light ray has entered from air to glass and has bent towards the normal that is from a rarer to denser medium.
(8) The light ray has emerged from glass to air that is from a denser medium to a rarer medium. The light here has bent away from the normal. Compare the angle of incidence with the angle of refraction at both refracting surfaces AB and CD.
(9) In Figure, EO is the incident ray OO' the refracted ray and O'H the emergent ray. You may observe that the emergent ray is parallel to the direction of the incident ray.
(10) The extent of bending of the ray of light at the opposite parallel faces AB (air-glass interface) and CD (glass-air-interface) of the rectangular glass slab is equal and opposite. This is why the ray emerges parallel to the incident ray.

Position of image
Object distance u = − 15 cm (to the left of mirror )
Image distance v = ?
Focal length f = − 10 cm (concave mirror) Using mirror formula.
\(\frac { 1 }{ v } +\frac { 1 }{ u } =\frac { 1 }{ f } \)
\(\frac { 1 }{ v } +\frac { 1 }{ -15 } =\frac { 1 }{ -10 } \)
\(\frac { 1 }{ v } -\frac { 1 }{ 15 } =\frac { -1 }{ 10 } \)
\(\frac { 1 }{ v } =\frac { -1 }{ 10 } +\frac { 1 }{ 15 } \)
\(\frac { 1 }{ v } =\frac { -1 }{ 30 } \)
∴ Image distance v = -30cm (negative sign indicates that the image is on the left side of the mirror)
∴ Position of image is 30 cm in front of the mirror
2.Nature of image: Since the image is in front of the mirror it is real and inverted.
3.Size of image: To find the size of the image, we have to calculate the magnification
\(m=\frac { -v }{ u } \)
Object distance u = − 15cm
Image distance v = − 30 cm 
\(m=\frac { -(-30) }{ (-15) } \)
m = − 2
We know that,\(m=\frac { { h }_{ 2 } }{ { h }_{ 1 } } \)
Here, height of the object h₁ = 1 cm
-2 =\(\frac { { h }_{ 2 } }{ 1 } \)
h₂ = -2\(\times\) 1
= -2 cm
The height of image is 2 cm (negative sign shows that the image is formed below the principal axis).

If the light rays coming from an object actually meet, after reflection, the image formed will be a real image and it is inverted. The real image can be produced on a screen.

A convex mirror is a spherical mirror whose reflecting surface is curved outward.

A spherical mirror whose reflecting surface is curved inwards is called a concave mirror.

Speed of light in vacuum is exactly 300,00 km / s

 
A ray passing through the principal focus of a concave mirror after reflection will emerge parallel to the principal axis.

1. Concave mirror
2. Concave mirror.

  Water, glass.

The spherical mirror equation is \(\frac { 1 }{ f } =\frac { 1 }{ { u } } +\frac { 1 }{ v } \)
u = distance of object.
v = distance of image.
f = focal length of spherical mirror.

Assertion is true but reason is false

Assertion is false but reason is true.