11 of a person standing in front of a plane mirror, the the mirror must be half the height of the person ▸ Spherical mirrors are the parts of a hollow glass sphere. They are of following two ▸ If the inner surface of the spherical mirror is the reflecting surface, then it is calle mirror. If the outer surface of the spherical mirror is the reflecting surface, then convex mirror >The centre of the sphere of which the mirror is a part, is called the centre of curva ▸ The centre of the surface of the mirror is called its pole (P) The radius of the sphere of which the mirror is a part, is called the radius of curva The straight line passing through the pole and centre of curvature is called the
****SPECIMEN QUESTIONS ****
(1) Which of the following relations is true for spherical mirrors?
(1)F= R 2
(2) F=2R R
(3) F=R
(4)F= 4
Explanation: The focal length of spherical mirror is half the radius of curvature. Option 1 is correct.
(2) -mirror is called converging mirror.
(1) Convex
(2) Plane
(3) Concave
(4) Any
Explanation: Concave mirror is called converging mirror because incident rays parallel to the principal axis after reflection from a concave mirror converge at a point. Option 3 is correct.
(3) Magnification obtained by a spherical mirror is 0.75. Which type of mirror it must be? (1) Concave
(2) Convex
(3) Plane
(4) cannot be determined
Explanation: Magnification is positive means that the image is erect and hence virtual. The absolute value of magnification is less than 1. It means that the image is diminished. Only convex mirror gives virtual and diminished image. So, the mirror must be convex. .
.Option 2 is correct.
(4) An object is kept at a distance of 25 cm from the convex mirror. If focal length of the convex mirror is 20 cm, find the distance of image from the mirror.
(1) 0.09cm (2) 0.01cm (3) 9 cm (4) 11.11 cm Explanation: u=-25 cm, f= 20 cm, v = ? 1 By mirror formula: + + vuf V -25 20 1 1 1 5+4 9 + V 20 25 100 100 100 V= 9 11.11 cm.
Option is correct.
QUESTIONS FOR PRACTICE
(1) The size of the image formed in a plane mirror is-
(1) larger than the object
(2) same as the object
(3) smaller than the object
(4) half the size of the object
Ana-(2) same as the object
(2) If the incident ray is parallel to the principal axis of a concave mirror, then the reflected ray-
(1) passes through principal focus.
(2) is parallel to the principal axis.
(3) passes through centre of curvature.
(4) follows the same path.
Ana-(1)basses through principal focus
(3) What is the correct mirror formula for a spherical mirror?
(1)__1___1_____1
______-____=
____v___u_____f
(2)1_____1_____1
_____-____=
___v_____u_____r
(3)1____1_____1
_____+____=
___v____u____r
(4)1____1____1
_____+_____=
____v___u___f
Ana-(4)1___1___1
_____+___
__v___u_|=f
(4) Dentists use- - mirror.
(1) plane
(2) concave
(3) convex
4) any
Ana-(2) concave
5) The magnification obtained by mirror is always positive and less than 1
. (1) plane
(2) concave
(3) convex
Ana-(4) spherical
convex
(6) If an object is placed between C and F of a concave mirror, then the image obtained is
(1) behind the mirror
2) at infinity
3) (3) beyond C
4) 4) at principal focus
Ana-(3) beyond C
(7) To get a virtual image in concave mirror, the object must be placed
(1) between P and F
(3) at C
(2) at F
(4) beyond C
Ana-(1) between P and F
(8) Concave mirror is not used for-
(1) shaving
(2) dentistry
(3) street lamp
(4) solar devices
Ana-(3) street lamp
(9) If an incident ray is passing through the principal focus of a concave mirror, then the reflected ray
(1) is parallel to the principal axis
(2) passes through the principal focus
(3) traces back the same path
(4) passes through the cer ature
Ana-(1) is parallel to the principal axis
(10) The distance between the principal focus and the pole of a mirror is called
(1) radius of curvature
(2) principal axis
(3) principal focus
(4) focal length
Ana-(4) focal length
(11) The image in a plane mirror is
(1) inverted
(2) laterally inverted
(3) real
(4) magnified
Ana-(2) laterally inverted
(12) A virtual image of a point object is formed when the reflected rays
(1) converge at a point
(2) appear to be coming from a point
(3) go parallel to each other
(4) trace the same path
Ana-(2) appear to be coming from a point
(13) The centre of the surface of the spherical mirror is called
(1) centre of curvature
(2) focus
(3) pole
(4) radius
Ana-(3) pole
(14) mirror is called a diverging mirror.
(1) Concave
(2) Plane
(3) Convex
(4) Spherical
Ana-(3) Convex
(15) The distance between the object and the pole is denoted by
(1)v
(2) u
(3)f
(4) M
Ana-(2) u
(16) Which of the following is the correct relation in context with spherical mirrors?
(1) M = h₁ h
(2) M=-2
(3) M = V u
(4) M=-
Ana- (4) M=---v
__________u
(17) The height of the object is always considered as
(1) positive
(2) negative
(3) zero
(4) whole number
Ana- (1) positive
(18) Which of the following statements is wrong?
(1) The focal length of concave mirror is negative
(2) The focal length of convex mirror is positive
(3) The vertical distances measured above the principal axis are positive
(4) The horizontal distances measured to the left of the pole are positive
Ana- (4) The horizontal distances measured to the left of the pole are positive
(19) The magnification obtained by a concave mirror is 4. If the height of the object is 10 cm what is the height of the image h, if the image is real?
(1) 40 cm
(2) 40 cm
(3) 2.5 cm
(4)-0.4 cm
Ana- (2) 40 cm
(20) To have a full image of a man of height 170 cm in a plane mirror, what should be the minimum height of the mirror?
(1) 170cm
(2) 340 cm
(3) 85 cm
(4) 17 cm
Ana -(3) 85 cm
Hints for difficult questions)
(8) In the street lamps, the reflectors are convex. .
.Option is correct.
(17) Object is always placed on the left side of the mirror and above the principal axis. The vertical distances measured above the principal axis are considered as positive as per the sign convention. .
.Option is correct.
(19) M = h₂ h₂ h₁ -4= 10 h₂ =-40 cm. .
.Option 2 is correct.
(20) To get the full image of an object, the minimum height of the plane mirror must be half the height of the object.
Option 3 is correct.
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