CBSE · Class 10

Physics Formulas — Class 10

All key physics formulas for CBSE Class 10 — electricity, light, magnetic effects, motion and energy for board exam preparation.

5 chapters27+ formulasCBSE 2026–27

Ch 1 Ch 2 Ch 3 Ch 4 Ch 5

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For reference only. Always verify formulas and information against your official NCERT textbooks or board-prescribed materials before use in exams. Learnizo does not guarantee absolute accuracy.

Ch 1.Electricity

Formula / Relation	Expression	Note
Ohm's Law	V = I × R	V = voltage (volts), I = current (amperes), R = resistance (ohms)
Resistance	R = V / I	Resistance is the ratio of voltage to current
Current	I = V / R	Current is directly proportional to voltage, inversely to resistance
Resistivity	R = ρ × L / A	ρ = resistivity, L = length of conductor, A = cross-sectional area
Resistors in Series	R_total = R₁ + R₂ + R₃ + ...	Total resistance is sum of individual resistances
Resistors in Parallel	1/R_total = 1/R₁ + 1/R₂ + 1/R₃ + ...	Equivalent resistance is always less than the smallest individual resistance
Electric Power	P = V × I = I²R = V²/R	P in watts (W), V in volts, I in amperes, R in ohms
Electrical Energy	E = P × t = V × I × t	E in joules (J) or kilowatt-hours (kWh); 1 kWh = 3.6 × 10⁶ J
Heat (Joule's Law)	H = I² × R × t	H = heat produced in joules, t = time in seconds

Ch 2.Light — Reflection (Mirrors)

Formula / Relation	Expression	Note
Mirror Formula	1/f = 1/v + 1/u	f = focal length, v = image distance, u = object distance (all measured from pole)
Magnification (mirror)	m = -v/u = h'/h	h' = image height, h = object height; m negative = inverted image; m positive = erect
Sign Convention	Distances along incident ray = positive; opposite = negative	Object is always placed to left; distances measured from pole
Focal length (concave)	f = R/2 (negative for concave)	R = radius of curvature; focal length of concave mirror is negative
Focal length (convex)	f = R/2 (positive for convex)	Convex mirror focal length is positive

Ch 3.Light — Refraction (Lenses)

Formula / Relation	Expression	Note
Lens Formula	1/f = 1/v - 1/u	Same sign convention as mirrors; f positive for convex lens, negative for concave
Magnification (lens)	m = v/u = h'/h	No negative sign unlike mirror formula
Power of Lens	P = 1/f	P in dioptres (D), f in metres; convex lens has positive power, concave negative
Combined Power	P = P₁ + P₂ + P₃ + ...	Powers of lenses in contact are additive
Snell's Law	n₁ sin θ₁ = n₂ sin θ₂	n = refractive index; at boundary between two media
Refractive Index	n = c/v = sin i / sin r	c = speed of light in vacuum, v = speed in medium; i = angle of incidence, r = angle of refraction

Ch 4.Magnetic Effects of Current

Formula / Relation	Expression	Note
Force on current-carrying conductor	F = BIL sin θ	B = magnetic field (tesla), I = current, L = length of conductor, θ = angle between B and I
Fleming's Left Hand Rule	Thumb = Force direction, Index = Field direction, Middle = Current direction	Used to find force direction on current in magnetic field
Fleming's Right Hand Rule	Thumb = Motion, Index = Field, Middle = Induced current	Used for electromagnetic induction (generator)

Ch 5.Motion (from Chapter 8 — if included in your exam)

Formula / Relation	Expression	Note
First equation of motion	v = u + at	v = final velocity, u = initial velocity, a = acceleration, t = time
Second equation of motion	s = ut + ½at²	s = displacement
Third equation of motion	v² = u² + 2as	Useful when time is not given
Average velocity	v_avg = (u + v)/2 = total displacement / total time	Only valid for uniform acceleration

Frequently Asked Questions

Which formulas are most important for Class 10 Physics board exam?

The highest-weightage chapter is Electricity — Ohm's Law, power formulas (P=VI, P=I²R), Joule's heating law, and series/parallel resistance calculations appear in almost every board paper. The mirror formula (1/f = 1/v + 1/u) and lens formula (1/f = 1/v - 1/u) with magnification are equally important. These five formula sets together cover approximately 20–25 marks of the Class 10 Science paper.

What is the difference between mirror formula and lens formula?

Mirror formula: 1/f = 1/v + 1/u (plus sign between 1/v and 1/u). Lens formula: 1/f = 1/v − 1/u (minus sign). The magnification formula also differs: mirror m = −v/u (note the negative sign); lens m = +v/u (no negative). The sign conventions are the same for both — distances measured from optical centre/pole, with the principal axis direction of incident light being positive.

How to remember the sign convention for optics?

Use the Cartesian sign convention: (1) All distances are measured from the optical centre/pole. (2) Distances in the direction of incident light (usually left to right) are positive. (3) Heights above principal axis are positive; below are negative. The incident ray always comes from the left. Object distance (u) is always negative (object is on the same side as incoming light, which is the negative direction).

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