Mirror formula and magnification: Class 10 practice
1/v + 1/u = 1/f with the New Cartesian sign convention (distances measured from the pole; in front of a mirror is negative). Read the method, follow the three worked examples, then try the six questions.
What you should know first
- Fractions
- Sign convention
The idea behind mirror formula and magnification
1/v + 1/u = 1/f with the New Cartesian sign convention (distances measured from the pole; in front of a mirror is negative). Magnification m = −v/u; negative m means real and inverted.
Step-by-step method
- Write u (negative for real objects) and f (negative for concave, positive for convex).
- Solve 1/v = 1/f − 1/u.
- m = −v/u; interpret sign and size.
Worked example 1 (Basic)
An object is 17 cm in front of a concave mirror of focal length 11 cm. Find the image distance.
- 1/v = 1/(-11) − 1/(-17)
- v = -31.17 cm
- Answer: v = -31.17 cm
Worked example 2 (Standard)
An object is 37 cm in front of a concave mirror of focal length 16 cm. Find the image distance and magnification.
- 1/v = 1/(-16) − 1/(-37)
- v = -28.19 cm
- m = -0.76 (real, inverted)
- Answer: v = -28.19 cm, m = -0.76
Worked example 3 (Challenge)
An object is 11 cm in front of a convex mirror of focal length 12 cm. Find the image position and magnification.
- 1/v = 1/12 − 1/(-11)
- v = 5.74 cm (behind the mirror, virtual)
- m = −v/u = 0.52
- Answer: v = 5.74 cm, m = 0.52
Common mistakes and misconceptions
- Taking u as positive
- Using the lens formula
Practice questions
- (Basic) An object is 27 cm in front of a concave mirror of focal length 15 cm. Find the image distance.
- (Basic) An object is 44 cm in front of a concave mirror of focal length 15 cm. Find the image distance.
- (Standard) An object is 44 cm in front of a concave mirror of focal length 17 cm. Find the image distance and magnification.
- (Standard) An object is 21 cm in front of a concave mirror of focal length 16 cm. Find the image distance and magnification.
- (Challenge) An object is 8 cm in front of a convex mirror of focal length 27 cm. Find the image position and magnification.
- (Challenge) An object is 26 cm in front of a convex mirror of focal length 19 cm. Find the image position and magnification.
Answer key with full working
- Q1: 1/v = 1/(-15) − 1/(-27) → v = -33.75 cm → Answer: v = -33.75 cm
- Q2: 1/v = 1/(-15) − 1/(-44) → v = -22.76 cm → Answer: v = -22.76 cm
- Q3: 1/v = 1/(-17) − 1/(-44) → v = -27.7 cm → m = -0.63 (real, inverted) → Answer: v = -27.7 cm, m = -0.63
- Q4: 1/v = 1/(-16) − 1/(-21) → v = -67.2 cm → m = -3.2 (real, inverted) → Answer: v = -67.2 cm, m = -3.2
- Q5: 1/v = 1/27 − 1/(-8) → v = 6.17 cm (behind the mirror, virtual) → m = −v/u = 0.77 → Answer: v = 6.17 cm, m = 0.77
- Q6: 1/v = 1/19 − 1/(-26) → v = 10.98 cm (behind the mirror, virtual) → m = −v/u = 0.42 → Answer: v = 10.98 cm, m = 0.42
Syllabus note
This skill is listed under "Light Reflection and Refraction" for Class 10 in the NCERT/CBSE books. ICSE, IGCSE, IB and state boards may teach it in a different chapter or year.
Answers on this page are generated and automatically re-checked by a second, independent calculation. They have not been reviewed by a teacher — if you spot a problem, tell us on WhatsApp.
Related practice and notes
- Light Reflection and Refraction chapter notes (Class 10)
- Refractive index and speed of light
- Power of a lens and lens combinations
- Snell's law
- Ohm's law and resistors in series and parallel
- Electric power and energy consumption
- Lens formula and magnification
- Resistivity and resistance of a wire
- All Class 10 practice
Frequently asked questions
Which chapter is mirror formula and magnification in?
"Light Reflection and Refraction", Class 10 Physics (NCERT/CBSE). Other boards may place it differently.
How were the answers checked?
Answers on this page are generated and automatically re-checked by a second, independent calculation. They have not been reviewed by a teacher — if you spot a problem, tell us on WhatsApp.