Concave and convex mirrors – Notes and Questions & Answers
POSITION OF IMAGE IN CASE OF CONCAVE MIRROR
| Position of image | Position of object | Size of image | Nature of image |
| At infinity | At focus F | Highly diminished, point size | Real and inverted |
| Beyond C | Between F and C | Diminished | Real and inverted |
| At C | At C | Same size | Real and inverted |
| Between C and F | Beyond C | Enlarged | Real and inverted |
| At F | At infinity | Highly enlarged | Real and inverted |
| Between F and P | Behind the mirror | Enlarged | Virtual and erect |
POSITION OF IMAGE IN CASE OF CONVEX MIRROR
| Position of image | Position of object | Size of image | Nature of image |
| At infinity | At focus F behind the mirror | Highly diminished, point size | Virtual and erect |
| Between infinity and P | Between P and F behind the mirror | Diminished | Virtual and erect |
Mirror Equation, sign convention and magnification formula for concave and convex mirror
Formula is same for concave and convex mirror but sign convention has to be used carefully
| Concave Mirror | Convex Mirror | |
|---|---|---|
| Focal Length ( f) | Negative (-) Focus is in front | Positive (+) Focus is behind |
| object distance (u) | Negative (-) (Always placed in front) | Negative (-) (Always placed in front) |
| image distance (v) | Negative (-) for Real images Positive (+) for Virtual images | Always Positive (+) (Images are always virtual and behind) |
NUMERICAL QUESTIONS ON CONCAVE MIRRORS
Position of image, object, focal length calculation using the Mirror Equation
- An object is placed 2 m in front of a concave mirror of focal length 1.5 m. The position of image will be?
Answer: – 6 m.(u = -2, f = -1.5) Image formed is Beyond C, Real & Inverted, and Enlarged
- An object placed 20 cm from the pole of a concave mirror forms real image at 60 cm from the pole. Focal length of the mirror is?
Answer: -15 cm.(u = -20, v = -60) Image formed is Beyond C, Real & Inverted, and Enlarged
- An object is placed 15 cm from a concave mirror having focal length of 10 cm. The position of image will be?
Answer: -30 cm. (u = -15, f = -10)Image formed is Beyond C, Real & Inverted, and Enlarged
- If object distance is 36 cm in front of a concave mirror of focal length 18 cm, where will the image be formed?
Answer: -36 cm. (u = -36, f = -18) Image is formed at C, Real & Inverted, and Enlarged
- If object distance is 24 cm in front of a concave mirror of focal length 12 cm, where will the image be formed?
Answer: -24 cm. (u = -24, f = -12) Image is formed at C, Real & Inverted, and Enlarged
- If object distance is 16 cm in front of a concave mirror of focal length 8 cm, where will the image be formed?
Answer: -16 cm. (u = -16, f = -8) Image is formed at C, Real & Inverted, and Enlarged
- What is the focal length of a concave mirror if an object placed at 18 cm produces image at 6 cm in front of the mirror?
Answer: -4.5 cm. (u = -18, v = -6) Image is formed between C and F, Real & Inverted, Diminished
- What is the focal length of a concave mirror if an object placed at 20 cm produces image at 5 cm in front of the mirror?
Answer: -4 cm. (u = -20, v = -5) Image is formed between C and F, Real & Inverted, Diminished
- If an object is placed at 18 cm in front of a concave mirror of focal length 6 cm. The image will be formed at?
Answer: -9 cm. (u = -18, f = -6) Image is formed between C and F, Real & Inverted, Diminished
- If object is placed at 6 cm in front of a concave mirror of focal length of 10 cm, the position of the image is?
Answer: +15 cm. (u =-6, f = -10) Image is formed behind mirror, Virtual & Erect, Enlarged
- If object is placed at 4 cm in front of a concave mirror of focal length of 8 cm, the position of the image is?
Answer: +8 cm. (u =-4, f = -8) Image is formed behind mirror, Virtual & Erect, Enlarged
- If object is placed at 5 cm in front of a concave mirror of focal length of 10 cm, the position of the image is?
Answer: +10 cm. (u =-5, f = -10) Image is formed behind mirror, Virtual & Erect, Enlarged
Magnification
- Calculate the magnification of an object kept 20 cm in front of a concave mirror which forms an image 60 cm in front of it.
Answer: -3. (u = -20, v = -60) Image formed is Real & Inverted, Three times enlarged
- Calculate the magnification of an object kept 10 cm in front of a concave mirror forms an image 30 cm in front of it.
Answer: -3. (u = -10, v = -30) Image formed is Real & Inverted, Three times enlarged
- Calculate the magnification of an object kept 15 cm in front of a concave mirror forms an image 45 cm in front of it.
Answer: -3. (u = -15, v = -45) Image formed is Real & Inverted, Three times enlarged
- If the image is formed at a distance of 6 cm and object is at 12 cm in front of a concave mirror, find the magnification?
Answer: -0.5. (u = -12, v = -6)Image is real & Inverted, Diminished by half
- If the image is formed at a distance of 7 cm and object is at 14 cm in front of a concave mirror, find the magnification?
Answer: -0.5. (u = -14, v = -7) Image is real & Inverted, Diminished by half
- If the image is formed at a distance of 8 cm and object is at 16 cm in front of a concave mirror, find the magnification?
Answer: -0.5. (u = -16, v = -8) Image is real & Inverted, Diminished by half
- If an object is placed 4 cm in front of a concave mirror and a virtual image is formed 8 cm behind the mirror find the magnification?
Answer: +2. (u = -4, v = -8) Image is Virtual & Erect, 2 times enlarged
NUMERICAL QUESTIONS ON CONVEX MIRRORS
Position of image, object, focal length calculation using the Mirror Equation
- An object is placed at a distance of 10 cm from the pole of a convex mirror of focal length 15 cm. The image will be formed at?
Answer: +6 cm. (u = -10, f = +15) Image is formed behind the mirror, Virtual & Erect, Diminished
- An object is placed at a distance of 10 cm from the pole of a convex mirror with radius of curvature of 30 cm. Image will be formed at?
Answer: +6 cm. (u = -10, f = +15) Image is formed behind the mirror, Virtual & Erect, Diminished
- An object is placed at a distance of 8 cm from the pole of a convex mirror of focal length 12 cm. The image will be formed at?
Answer: +4.8 cm. (u = -8, f = +12) Image is formed behind the mirror, Virtual & Erect, Diminished
- Find the position of the image of an object placed at a distance of 6 m from a convex mirror of focal length 2 m.
Answer: +1.5 m. (u = -6, f = +2) Image formed behind the mirror is, Virtual & Erect, Diminished
- Find the position of the image of an object placed at a distance of 6 m from a convex mirror of focal length 4 m.
Answer: +2.4 m. (u = -6, f = +4) Image formed behind the mirror is, Virtual & Erect, Diminished
- Find the position of the image of an object placed at a distance of 6 m from a convex mirror of focal length 3 m.
Answer: +2 m. (u = -6, f = +3) Image formed behind the mirror is, Virtual & Erect, Diminished
- A rear view convex mirror has a radius of curvature of 6 m. If a car is located at 7 m from it, the position of the image is?
Answer: +2.1 m. (u = -7, f = +3) Image formed behind the mirror is, Virtual & Erect, Diminished
- A rear view convex mirror has a radius of curvature of 4 m. If a car is located at 8 m from it, the position of the image is?
Answer: +1.6 m. (u = -8, f = +2) Image formed behind the mirror is, Virtual & Erect, Diminished
- A rear view convex mirror has a radius of curvature of 4 m. If a car is located at 6 m from it, the position of the image is?
Answer: +1.5 m. (u = -6, f = +2) Image formed behind the mirror is, Virtual & Erect, Diminished
Magnification
- Find the magnification if an object kept 30 cm in front of a convex mirror produces virtual image at 12 cm behind the mirror.
Answer: +0.4. (u = -30; v = +12) Image is Virtual & Erect, Diminished by 2/5th
- Find the magnification if an object kept 20 cm in front of a convex mirror produces virtual image at 8 cm behind the mirror.
Answer: +0.4. (u = -20; v = +8) Image is Virtual & Erect, Diminished by 2/5th
- Find the magnification if an object kept 15 cm in front of a convex mirror produces virtual image at 6 cm behind the mirror.
Answer: +0.4. (u = -15; v = +6) Image is Virtual & Erect, Diminished by 2/5th