Physics Formulae
Essential formulae for CBSE Class 10 โข First 2 chapters FREE!
Chapter 1: Light - Reflection and Refraction
Mirror Formula
1/v + 1/u = 1/f
Relates object distance (u), image distance (v), and focal length (f) for spherical mirrors. All distances measured from...
๐ก Example:
Problem: Object at 20 cm from concave mirror (f = -10 cm). Find image position.
Solution:
u = -20 c...
Solution:
u = -20 c...
Magnification (Mirror)
m = h'/h = -v/u
Magnification is ratio of image height (h') to object height (h). For mirrors: m = -v/u. Negative m means inverted image...
๐ก Example:
Problem: v = -30 cm, u = -10 cm. Find magnification.
Solution:
m = -v/u = -(-30)/(-10) = -3
Image ...
Solution:
m = -v/u = -(-30)/(-10) = -3
Image ...
Lens Formula
1/v - 1/u = 1/f
Relates object distance (u), image distance (v), and focal length (f) for thin lenses. Sign convention: f is +ve for con...
๐ก Example:
Problem: Object at 30 cm from convex lens (f = +15 cm). Find image.
Solution:
u = -30 cm, f = +15 c...
Solution:
u = -30 cm, f = +15 c...
Magnification (Lens)
m = h'/h = v/u
For lenses: m = v/u (no negative sign unlike mirrors). Positive m = erect image, negative m = inverted image.
๐ก Example:
Problem: u = -30 cm, v = +60 cm. Find magnification.
Solution:
m = v/u = 60/(-30) = -2
Image is 2 ...
Solution:
m = v/u = 60/(-30) = -2
Image is 2 ...
Snell's Law (Refractive Index)
n = sin i / sin r = c/v = ฮปโ/ฮปโ
Refractive index relates angle of incidence (i) and refraction (r). Also equals ratio of speed of light in vacuum (c) to...
๐ก Example:
Problem: Light enters glass (n = 1.5) at 45ยฐ. Find angle of refraction.
Solution:
n = sin i / sin ...
Solution:
n = sin i / sin ...
Power of Lens
P = 1/f (f in metres), Unit: Dioptre (D)
Power measured in Dioptres (D). P is +ve for convex (converging), -ve for concave (diverging). When lenses combined: P_t...
๐ก Example:
Problem: Lens has f = 50 cm. Find power.
Solution:
f = 50 cm = 0.5 m
P = 1/0.5 = +2 D (convex lens)...
Solution:
f = 50 cm = 0.5 m
P = 1/0.5 = +2 D (convex lens)...
Relationship: Focal Length & Radius of Curvature
f = R/2 or R = 2f
For spherical mirrors, focal length is half the radius of curvature. Centre of curvature (C) is at distance R from pole,...
๐ก Example:
Problem: Concave mirror has R = 30 cm. Find f.
Solution:
f = R/2 = 30/2 = 15 cm
Since concave: f =...
Solution:
f = R/2 = 30/2 = 15 cm
Since concave: f =...
Critical Angle Formula
sin C = 1/n (or n = 1/sin C)
Critical angle is angle of incidence in denser medium for which angle of refraction is 90ยฐ. Total Internal Reflection o...
๐ก Example:
Problem: Glass has n = 1.5. Find critical angle.
Solution:
sin C = 1/n = 1/1.5 = 0.667
C = sinโปยน...
Solution:
sin C = 1/n = 1/1.5 = 0.667
C = sinโปยน...
Lens Maker's Formula
1/f = (n-1)(1/Rโ - 1/Rโ)
Relates focal length to refractive index (n) and radii of curvature (Rโ, Rโ) of lens surfaces. For equi-convex lens:...
๐ก Example:
Problem: Equi-convex lens, R = 20 cm, n = 1.5. Find f.
Solution:
1/f = (1.5-1)(1/20 - 1/(-20))
1/f ...
Solution:
1/f = (1.5-1)(1/20 - 1/(-20))
1/f ...
Combination of Thin Lenses
1/f = 1/fโ + 1/fโ (or P = Pโ + Pโ)
When thin lenses are in contact, their powers add up. Equivalent focal length found by adding reciprocals.
๐ก Example:
Problem: Convex lens (fโ = +20 cm) and concave lens (fโ = -30 cm) in contact.
Solution:
1/f = 1...
Solution:
1/f = 1...
Chapter 3: Electricity
Ohm's Law
V = IR (Voltage = Current ร Resistance)
Electrical Power
P = VI = IยฒR = Vยฒ/R (Unit: Watt)
Electrical Energy
E = Pt = VIt = IยฒRt (Unit: Joule or kWh)
Resistors in Series
R_eq = Rโ + Rโ + Rโ + ...
Physics Questions
Practice with CBSE pattern questions โข Free chapters unlocked!
Ch 1: Light - Reflection and Refraction
Q. The focal length of a plane mirror is:
Ch 1: Light - Reflection and Refraction
Q. A concave mirror has focal length of 15 cm. What is its radius of curvature?
Ch 1: Light - Reflection and Refraction
Q. Which mirror is used by dentists to examine teeth?
Ch 1: Light - Reflection and Refraction
Q. The image formed by a convex mirror is always:
Ch 1: Light - Reflection and Refraction
Q. If the magnification produced by a mirror is +2, the image is:
Ch 1: Light - Reflection and Refraction
Q. The power of a convex lens of focal length 25 cm is:
Ch 1: Light - Reflection and Refraction
Q. Which of the following can make a parallel beam of light converge at a point?
Ch 1: Light - Reflection and Refraction
Q. The speed of light in vacuum is 3 ร 10โธ m/s. If the refractive index of a medium is 1.5, the speed of light in that medium is:
Ch 1: Light - Reflection and Refraction
Q. Define the term "power of a lens". What is its SI unit?
Ch 1: Light - Reflection and Refraction
Q. State Snell's law of refraction.
Ch 3: Electricity
Q. The SI unit of electric current is:
Ch 3: Electricity
Q. Two resistors of 4ฮฉ and 6ฮฉ are connected in parallel. The equivalent resistance is:
Ch 3: Electricity
Q. If the resistance of a conductor is doubled and voltage remains same, the current will:
Ch 3: Electricity
Q. An electric heater draws 2A current from 220V supply. The power of heater is:
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