Solution : Given,
Focal length of concave mirror cm
Real image is four times the size of object
Magnification, m = −4
m = - v / u
Using mirror formula,
1/f = 1/v + 1/u
Distance of object = 12.5 cm
Ans: D) 12.5 cm
Soln
f = 30/2 = 15 cm
Q: Object at infinity in concave mirror forms image where ?
Ans: At focus.
āĻĒā§ā§°āĻļā§āĻ¨: āĻ
āĻ¸ā§āĻŽ āĻĻā§ā§°āĻ¤ āĻŦāĻ¸ā§āĻ¤ā§ āĻĨāĻžāĻāĻŋāĻ˛ā§ āĻ
ā§ąāĻ¤āĻ˛ āĻĻā§°ā§āĻĒāĻŖā§ āĻĒā§ā§°āĻ¤āĻŋāĻŦāĻŋāĻŽā§āĻŦ āĻ’āĻ¤ āĻāĻ āĻ¨ āĻā§°ā§ ?
āĻāĻ¤ā§āĻ¤ā§°: āĻĢā§āĻāĻžāĻāĻ¤āĨ¤
Q: Which mirror is used as rear-view mirror and why ?
Ans: Convex mirror, wide field of view.
āĻĒā§ā§°āĻļā§āĻ¨: ā§°āĻŋāĻ¯āĻŧāĻžā§°-āĻāĻŋāĻ āĻŽāĻŋā§°ā§° āĻšāĻŋāĻāĻžāĻĒā§ āĻā§āĻ¨āĻā§ āĻĻā§°ā§āĻĒāĻŖ āĻŦā§āĻ¯ā§ąāĻšāĻžā§° āĻā§°āĻž āĻšāĻ¯āĻŧ āĻā§°ā§ āĻāĻŋāĻ¯āĻŧ ?
āĻāĻ¤ā§āĻ¤ā§°: āĻāĻ¤ā§āĻ¤āĻ˛ āĻĻā§°ā§āĻĒāĻŖ, āĻŦā§āĻāĻŋ āĻĻā§āĻļā§āĻ¯ āĻā§āĻˇā§āĻ¤ā§ā§°āĨ¤
Q: Find magnification if hi = 6 cm, ho = 3 cm.
Soln
m = 6/3 = 2
āĻĒā§ā§°āĻļā§āĻ¨: hi = 6 cm, ho = 3 cm āĻšāĻ˛ā§ āĻŦāĻĸāĻŧāĻžā§ą āĻāĻŋāĻŽāĻžāĻ¨ ?
āĻāĻ¤ā§āĻ¤ā§°: 2
Q: An image formed by concave mirror is virtual. Where is object ?
Ans: Between pole and focus.
āĻĒā§ā§°āĻļā§āĻ¨: āĻ
ā§ąāĻ¤āĻ˛ āĻĻā§°ā§āĻĒāĻŖā§ āĻāĻžā§°ā§āĻā§ā§ąā§āĻ˛ āĻĒā§ā§°āĻ¤āĻŋāĻŦāĻŋāĻŽā§āĻŦ āĻāĻ āĻ¨ āĻā§°āĻŋāĻ˛ā§ āĻŦāĻ¸ā§āĻ¤ā§ āĻ’āĻ¤ āĻĨāĻžāĻā§ ?
āĻāĻ¤ā§āĻ¤ā§°: āĻĒ’āĻ˛ āĻā§°ā§ āĻĢā§āĻāĻžāĻā§° āĻŽāĻžāĻāĻ¤āĨ¤
Q: Write sign of focal length of concave mirror.
Ans: Negative.
āĻĒā§ā§°āĻļā§āĻ¨: āĻ
ā§ąāĻ¤āĻ˛ āĻĻā§°ā§āĻĒāĻŖā§° āĻĢā§āĻāĻžāĻ˛ āĻĻā§ā§°ā§āĻā§āĻ¯ā§° āĻāĻŋāĻšā§āĻ¨ āĻāĻŋ ?
āĻāĻ¤ā§āĻ¤ā§°: āĻāĻŖāĻžāĻ¤ā§āĻŽāĻāĨ¤
Q: A mirror has f = –20 cm. Identify mirror.
Ans: Concave mirror.
āĻĒā§ā§°āĻļā§āĻ¨: f = –20 cm āĻĨāĻāĻž āĻĻā§°ā§āĻĒāĻŖāĻā§ āĻā§āĻ¨āĻā§ ?
āĻāĻ¤ā§āĻ¤ā§°: āĻ
ā§ąāĻ¤āĻ˛ āĻĻā§°ā§āĻĒāĻŖāĨ¤
Q: If magnification is +1, image is ?
Ans: Virtual and same size.
āĻĒā§ā§°āĻļā§āĻ¨: āĻŦāĻĸāĻŧāĻžā§ą +1 āĻšāĻ˛ā§ āĻĒā§ā§°āĻ¤āĻŋāĻŦāĻŋāĻŽā§āĻŦ āĻā§āĻ¨ā§ ?
āĻāĻ¤ā§āĻ¤ā§°: āĻāĻžā§°ā§āĻā§ā§ąā§āĻ˛ āĻā§°ā§ āĻāĻā§ āĻāĻāĻžā§°ā§°āĨ¤
Q: State two uses of concave mirror.
Ans: Headlights, shaving mirror.
āĻĒā§ā§°āĻļā§āĻ¨: āĻ
ā§ąāĻ¤āĻ˛ āĻĻā§°ā§āĻĒāĻŖā§° āĻĻā§āĻāĻž āĻŦā§āĻ¯ā§ąāĻšāĻžā§° āĻ˛āĻŋāĻāĻžāĨ¤
āĻāĻ¤ā§āĻ¤ā§°: āĻāĻžāĻĄāĻŧā§ā§° āĻšā§āĻĄāĻ˛āĻžāĻāĻ, āĻļā§āĻāĻŋāĻ āĻŽāĻŋā§°ā§°āĨ¤
Q: State two uses of convex mirror.
Ans: Rear-view mirror, security mirror.
āĻĒā§ā§°āĻļā§āĻ¨: āĻāĻ¤ā§āĻ¤āĻ˛ āĻĻā§°ā§āĻĒāĻŖā§° āĻĻā§āĻāĻž āĻŦā§āĻ¯ā§ąāĻšāĻžā§° āĻ˛āĻŋāĻāĻžāĨ¤
āĻāĻ¤ā§āĻ¤ā§°: ā§°āĻŋāĻ¯āĻŧāĻžā§°-āĻāĻŋāĻ āĻŽāĻŋā§°ā§°, āĻā§ā§°āĻŋ ā§°ā§āĻ§ āĻĻā§°ā§āĻĒāĻŖāĨ¤
Q: Object distance is –15 cm and image distance –30 cm. Find magnification.
Soln
m = −v/u = −30/−15 = −2
āĻĒā§ā§°āĻļā§āĻ¨: u = –15 cm, v = –30 cm āĻšāĻ˛ā§ āĻŦāĻĸāĻŧāĻžā§ą āĻāĻŋāĻŽāĻžāĻ¨ ?
āĻāĻ¤ā§āĻ¤ā§°: –2
Q: Image formed at infinity by concave mirror. Where is object ?
Ans: At focus.
āĻĒā§ā§°āĻļā§āĻ¨: āĻĒā§ā§°āĻ¤āĻŋāĻŦāĻŋāĻŽā§āĻŦ āĻ
āĻ¸ā§āĻŽāĻ¤ āĻāĻ āĻ¨ āĻšāĻ˛ā§ āĻŦāĻ¸ā§āĻ¤ā§ āĻ’āĻ¤ āĻĨāĻžāĻā§ ?
āĻāĻ¤ā§āĻ¤ā§°: āĻĢā§āĻāĻžāĻāĻ¤āĨ¤
Q: Write nature of image formed by convex mirror.
Ans: Virtual, erect, diminished.
āĻĒā§ā§°āĻļā§āĻ¨: āĻāĻ¤ā§āĻ¤āĻ˛ āĻĻā§°ā§āĻĒāĻŖā§° āĻĒā§ā§°āĻ¤āĻŋāĻŦāĻŋāĻŽā§āĻŦā§° āĻ¸ā§āĻŦāĻāĻžā§ą āĻ˛āĻŋāĻāĻžāĨ¤
āĻāĻ¤ā§āĻ¤ā§°: āĻāĻžā§°ā§āĻā§ā§ąā§āĻ˛, āĻ¸ā§āĻāĻž, āĻ¸ā§°ā§āĨ¤
Q: Define magnification. āĻĒā§ā§°āĻļā§āĻ¨: āĻŦāĻĸāĻŧāĻžā§ą āĻ¸āĻāĻā§āĻāĻž āĻĻāĻŋāĻ¯āĻŧāĻžāĨ¤
Ans: Ratio of height of image to height of object.
Q: Find the focal length of a mirror whose radius of curvature is 50 cm.
Solution: f = R/2 = 25f = R/2 = 25 cm
āĻĒā§ā§°āĻļā§āĻ¨ (Ass): āĻŦāĻā§ā§°āĻ¤āĻžā§° āĻŦā§āĻ¯āĻžāĻ¸āĻžā§°ā§āĻ§ 50 cm āĻšāĻ˛ā§ āĻĢā§āĻāĻžāĻ˛ āĻĻā§ā§°ā§āĻā§āĻ¯ āĻāĻŋāĻŽāĻžāĻ¨?
āĻāĻ¤ā§āĻ¤ā§°: 25 cm
Q: Name the mirror that can form a real image.
Ans: Concave mirror
āĻĒā§ā§°āĻļā§āĻ¨: āĻĒā§ā§°āĻā§āĻ¤ āĻĒā§ā§°āĻ¤āĻŋāĻŦāĻŋāĻŽā§āĻŦ āĻāĻ āĻ¨ āĻā§°āĻŋāĻŦ āĻĒā§°āĻž āĻĻā§°ā§āĻĒāĻŖā§° āĻ¨āĻžāĻŽ āĻ˛āĻŋāĻāĻžāĨ¤
āĻāĻ¤ā§āĻ¤ā§°: āĻ
ā§ąāĻ¤āĻ˛ āĻĻā§°ā§āĻĒāĻŖ
Q: An object is placed between F and P of a concave mirror. State image nature.
Ans: Virtual, erect, enlarged
āĻĒā§ā§°āĻļā§āĻ¨: āĻ
ā§ąāĻ¤āĻ˛ āĻĻā§°ā§āĻĒāĻŖā§° F āĻā§°ā§ P ā§° āĻŽāĻžāĻāĻ¤ āĻŦāĻ¸ā§āĻ¤ā§ ā§°āĻžāĻāĻŋāĻ˛ā§ āĻĒā§ā§°āĻ¤āĻŋāĻŦāĻŋāĻŽā§āĻŦā§° āĻ¸ā§āĻŦāĻāĻžā§ą āĻāĻŋ?
āĻāĻ¤ā§āĻ¤ā§°: āĻāĻžā§°ā§āĻā§ā§ąā§āĻ˛, āĻ¸ā§āĻāĻž, āĻĄāĻžāĻā§°
Q: Write formula for magnification of mirror.
Ans: m = -v/u
āĻĒā§ā§°āĻļā§āĻ¨: āĻĻā§°ā§āĻĒāĻŖā§° āĻŦāĻĸāĻŧāĻžā§ąā§° āĻ¸ā§āĻ¤ā§ā§° āĻ˛āĻŋāĻāĻžāĨ¤
āĻāĻ¤ā§āĻ¤ā§°: m = -v/u
Q: If object height = 2 cm and image height = –6 cm, find magnification.
Soln
m = -6/2 = -3
āĻĒā§ā§°āĻļā§āĻ¨: āĻŦāĻ¸ā§āĻ¤ā§ā§° āĻāĻā§āĻāĻ¤āĻž 2 cm āĻā§°ā§ āĻĒā§ā§°āĻ¤āĻŋāĻŦāĻŋāĻŽā§āĻŦā§° āĻāĻā§āĻāĻ¤āĻž –6 cm āĻšāĻ˛ā§ āĻŦāĻĸāĻŧāĻžā§ą āĻāĻŋāĻŽāĻžāĻ¨ ?
āĻāĻ¤ā§āĻ¤ā§°: –3
Q: Which mirror has positive focal length ?
Ans: Convex mirror
āĻĒā§ā§°āĻļā§āĻ¨: āĻā§āĻ¨āĻā§ āĻĻā§°ā§āĻĒāĻŖā§° āĻĢā§āĻāĻžāĻ˛ āĻĻā§ā§°ā§āĻā§āĻ¯ āĻ§āĻ¨āĻžāĻ¤ā§āĻŽāĻ ?
āĻāĻ¤ā§āĻ¤ā§°: āĻāĻ¤ā§āĻ¤āĻ˛ āĻĻā§°ā§āĻĒāĻŖ
Q: State sign of image distance for real image.
Ans: Negative
āĻĒā§ā§°āĻļā§āĻ¨: āĻĒā§ā§°āĻā§āĻ¤ āĻĒā§ā§°āĻ¤āĻŋāĻŦāĻŋāĻŽā§āĻŦā§° āĻŦāĻžāĻŦā§ v ā§° āĻāĻŋāĻšā§āĻ¨ āĻāĻŋ ?
āĻāĻ¤ā§āĻ¤ā§°: āĻāĻŖāĻžāĻ¤ā§āĻŽāĻ
Q: Find image distance if f = –10 cm, u = –20 cm.
Soln
1/−10 = 1/v + 1/−20
⇒1/v = −1/20
⇒ v = −20 cm
āĻāĻ¤ā§āĻ¤ā§°: –20 cm
Q: What happens to image size when object approaches focus of concave mirror ?
Ans: Image becomes larger.
āĻĒā§ā§°āĻļā§āĻ¨: āĻŦāĻ¸ā§āĻ¤ā§ āĻĢā§āĻāĻžāĻā§° āĻāĻā§°āĻ˛ā§ āĻāĻšāĻŋāĻ˛ā§ āĻĒā§ā§°āĻ¤āĻŋāĻŦāĻŋāĻŽā§āĻŦā§° āĻāĻāĻžā§° āĻāĻŋ āĻšāĻ¯āĻŧ ?
āĻāĻ¤ā§āĻ¤ā§°: āĻĄāĻžāĻā§° āĻšāĻ¯āĻŧāĨ¤
Ans: Concave mirror
āĻĒā§ā§°āĻļā§āĻ¨: āĻ’āĻ˛āĻžā§° āĻā§āĻāĻžā§°āĻ¤ āĻŦā§āĻ¯ā§ąāĻšāĻžā§° āĻā§°āĻž āĻĻā§°ā§āĻĒāĻŖāĻā§ āĻā§āĻ¨āĻā§ ?
āĻāĻ¤ā§āĻ¤ā§°: āĻ
ā§ąāĻ¤āĻ˛ āĻĻā§°ā§āĻĒāĻŖ
Q: Image formed by convex mirror is always where ?
Ans: Behind the mirror
āĻĒā§ā§°āĻļā§āĻ¨: āĻāĻ¤ā§āĻ¤āĻ˛ āĻĻā§°ā§āĻĒāĻŖā§° āĻĒā§ā§°āĻ¤āĻŋāĻŦāĻŋāĻŽā§āĻŦ āĻ¸āĻĻāĻžāĻ¯āĻŧ āĻ’āĻ¤ āĻāĻ āĻ¨ āĻšāĻ¯āĻŧ ?
āĻāĻ¤ā§āĻ¤ā§°: āĻĻā§°ā§āĻĒāĻŖā§° āĻĒāĻžāĻāĻĢāĻžāĻ˛ā§
Q: What is principal axis ?
Ans: Line passing through pole and centre of curvature.
āĻĒā§ā§°āĻļā§āĻ¨: āĻĒā§ā§°āĻ§āĻžāĻ¨ āĻ
āĻā§āĻˇ āĻāĻŋ ?
āĻāĻ¤ā§āĻ¤ā§°: āĻĒ’āĻ˛ āĻā§°ā§ āĻŦāĻā§ā§°āĻ¤āĻžā§° āĻā§āĻ¨ā§āĻĻā§ā§°ā§° āĻŽāĻžāĻā§āĻĻāĻŋ āĻ¯ā§ā§ąāĻž ā§°ā§āĻāĻžāĨ¤
Q: Write SI unit of focal length.
Ans: metre (m)
āĻĒā§ā§°āĻļā§āĻ¨: āĻĢā§āĻāĻžāĻ˛ āĻĻā§ā§°ā§āĻā§āĻ¯ā§° SI āĻāĻāĻ āĻāĻŋ ?
āĻāĻ¤ā§āĻ¤ā§°: āĻŽāĻŋāĻāĻžā§° (m)
Q: Name mirror used in torch light.
Ans: Concave mirror
āĻĒā§ā§°āĻļā§āĻ¨: āĻā§°ā§āĻ āĻ˛āĻžāĻāĻāĻ¤ āĻŦā§āĻ¯ā§ąāĻšāĻžā§° āĻā§°āĻž āĻĻā§°ā§āĻĒāĻŖ āĻā§āĻ¨āĻā§ ?
āĻāĻ¤ā§āĻ¤ā§°: āĻ
ā§ąāĻ¤āĻ˛ āĻĻā§°ā§āĻĒāĻŖ
Q: An object is placed at the centre of curvature of a concave mirror. Where is the image formed ?
Ans: At centre of curvature, real, inverted, same size.
āĻĒā§ā§°āĻļā§āĻ¨ (Ass): āĻ
ā§ąāĻ¤āĻ˛ āĻĻā§°ā§āĻĒāĻŖā§° āĻŦāĻā§ā§°āĻ¤āĻžā§° āĻā§āĻ¨ā§āĻĻā§ā§°āĻ¤ āĻŦāĻ¸ā§āĻ¤ā§ ā§°āĻžāĻāĻŋāĻ˛ā§ āĻĒā§ā§°āĻ¤āĻŋāĻŦāĻŋāĻŽā§āĻŦ āĻ’āĻ¤ āĻāĻ āĻ¨ āĻšāĻ¯āĻŧ ?
āĻāĻ¤ā§āĻ¤ā§°: āĻŦāĻā§ā§°āĻ¤āĻžā§° āĻā§āĻ¨ā§āĻĻā§ā§°āĻ¤ā§āĻ, āĻĒā§ā§°āĻā§āĻ¤, āĻāĻ˛ā§āĻāĻž, āĻāĻā§ āĻāĻāĻžā§°ā§°āĨ¤
Q: Write the mirror formula. āĻĒā§ā§°āĻļā§āĻ¨: āĻĻā§°ā§āĻĒāĻŖ āĻ¸āĻŽā§āĻā§°āĻŖ āĻ˛āĻŋāĻāĻžāĨ¤
Ans: 1/f = 1/v + 1/u
āĻāĻ¤ā§āĻ¤ā§°: āĻĒā§ā§°āĻ¤āĻŋāĻŦāĻŋāĻŽā§āĻŦā§° āĻāĻā§āĻāĻ¤āĻž āĻā§°ā§ āĻŦāĻ¸ā§āĻ¤ā§ā§° āĻāĻā§āĻāĻ¤āĻžā§° āĻ āĻ¨ā§āĻĒāĻžāĻ¤āĨ¤
Q: A concave mirror forms a real image. What is the sign of magnification ?
Ans: Negative.
āĻĒā§ā§°āĻļā§āĻ¨: āĻ
ā§ąāĻ¤āĻ˛ āĻĻā§°ā§āĻĒāĻŖā§ āĻĒā§ā§°āĻā§āĻ¤ āĻĒā§ā§°āĻ¤āĻŋāĻŦāĻŋāĻŽā§āĻŦ āĻāĻ āĻ¨ āĻā§°āĻŋāĻ˛ā§ āĻŦāĻĸāĻŧāĻžā§ąā§° āĻāĻŋāĻšā§āĻ¨ āĻāĻŋ ?
āĻāĻ¤ā§āĻ¤ā§°: āĻāĻŖāĻžāĻ¤ā§āĻŽāĻ (–)āĨ¤
Q: Why is concave mirror used by dentists ?
Ans: To get enlarged, upright image.
āĻĒā§ā§°āĻļā§āĻ¨: āĻĻāĻ¨ā§āĻ¤ āĻāĻŋāĻāĻŋā§āĻ¸āĻā§ āĻ
ā§ąāĻ¤āĻ˛ āĻĻā§°ā§āĻĒāĻŖ āĻāĻŋāĻ¯āĻŧ āĻŦā§āĻ¯ā§ąāĻšāĻžā§° āĻā§°ā§ ?
āĻāĻ¤ā§āĻ¤ā§°: āĻĄāĻžāĻā§° āĻā§°ā§ āĻ¸ā§āĻāĻž āĻĒā§ā§°āĻ¤āĻŋāĻŦāĻŋāĻŽā§āĻŦ āĻĒāĻžāĻŦāĻ˛ā§āĨ¤
Q: A convex mirror always forms which type of image ?
Ans: Virtual, erect, diminished.
āĻĒā§ā§°āĻļā§āĻ¨: āĻāĻ¤ā§āĻ¤āĻ˛ āĻĻā§°ā§āĻĒāĻŖā§ āĻ¸āĻĻāĻžāĻ¯āĻŧ āĻā§āĻ¨ā§ āĻĒā§ā§°āĻ¤āĻŋāĻŦāĻŋāĻŽā§āĻŦ āĻāĻ āĻ¨ āĻā§°ā§ ?
āĻāĻ¤ā§āĻ¤ā§°: āĻāĻžā§°ā§āĻā§ā§ąā§āĻ˛, āĻ¸ā§āĻāĻž, āĻ¸ā§°ā§āĨ¤
Q: Write relation between focal length and radius of curvature.
Ans: f = R/2
āĻĒā§ā§°āĻļā§āĻ¨: āĻĢā§āĻāĻžāĻ˛ āĻĻā§ā§°ā§āĻā§āĻ¯ āĻā§°ā§ āĻŦāĻā§ā§°āĻ¤āĻžā§° āĻŦā§āĻ¯āĻžāĻ¸āĻžā§°ā§āĻ§ā§° āĻ¸āĻŽā§āĻĒā§°ā§āĻ āĻ˛āĻŋāĻāĻžāĨ¤
āĻāĻ¤ā§āĻ¤ā§°: f = R/2