Establish the relationship between radius of curvature (r) and focal length (f) for a convex mirror. Write one use of a concave mirror. [2+1]
WBBSE
Class X
Physical Science
Light – Reflection and Refraction
03 Mark
2026
Let P, F and C be the pole, focus and centre of curvature of the convex mirror.
According to the law of reflection, ∠MQC’ = ∠NQC’
Since MQ ∥ PC, ∠CQC’ = ∠FCQ
Therefore, ∠FCQ = ∠FQC
Hence, FC = FQ
For paraxial rays, FQ ≈ FP = f
Therefore, FC = FP = f
Now, CP = CF + FP = 2f
Since CP = r,
r = 2f or, f = \frac{\text{r}}{2}
Use of concave mirror: It is used as a reflector in vehicle headlights.
Related Questions
More WBBSE Moderate level questions
1/12
Q.
Draw refracted rays for the incident rays which are parallel to the principal axis of...
A.
Ray Diagram for convex lens: OR Converging action of the convex lens...
Q.
A light is incident from air medium on another medium. If the refractive index of...
A.
Finding the wavelength: μ = 1.5 λmedium = 4000 Å λair =...
Q.
A convex lens forms a 10 times magnified image of an object. If the length...
A.
Magnification (m) = 10 Height of object (h₁) = 5 cm Height...
Q.
At what angle must a light ray fall on the surface of an equilateral prism...
A.
Angle of the prism = 60° Angle of minimum deviation (δ) =...
Q.
The magnified virtual image is formed by (a) convex mirror (b) convex lens (c) plane...
A.
(d) concave lens Explanation A concave lens forms a magnified virtual image...
Q.
The equation expressing the correlation between refractive index and wavelength of light is (a) μ...
A.
(d) μ = A + B/λ² Explanation The refractive index (μ) of...
Q.
If a reflected ray from a concave mirror makes an angle of 45° with the...
A.
d. 45° Explanation: According to the law of reflection, the angle of...
Q.
Write two causes of short-sightedness or myopia. Which type of lens is used to correct...
A.
Myopia may occur due to: Excessive curvature of the eye lens, which...
Q.
For the same angle of incidence, the angles of refraction in three different media A,...
A.
For the same angle of incidence, Angle of refraction in medium A...
Q.
Define dispersion of light. How would you identify monochromatic light and composite light with the...
A.
Dispersion of Light is the phenomenon where light splits into its constituent...
Q.
Write down the relationship between relative refractive index and absolute refractive index. On which factors...
A.
Relative refractive index of medium 2 with respect to medium 1: 1μ2...
Q.
In the case of refraction if the angle of incidence is 45° and the refracted...
A.
Angle of incidence (i) = 45º Angle of refraction (r) = 60º...