Class 10 Physics All Formulas PDF: Light, Eye and Electricity

This class 10 physics all formulas PDF page brings together the formulas of the light and electricity chapters in Class 10 science, with Ohm's law, $V = IR$ , as the one you will use most. Print the page from your browser and pick save as PDF to keep an offline copy for revision.

Class 10 physics in the NCERT science book has four chapters: light (reflection and refraction), the human eye and the colourful world, electricity, and magnetic effects of electric current. Mirrors and lenses use the New Cartesian sign convention, so any distance measured opposite to the incoming light gets a minus sign. Want the class 9 physics all formulas PDF as well, or a list of all physics formulas PDF style for the next level? There is a Class 9 table further down, and older students can turn to the Class 11 chapter wise list, the Class 12 sheet and the formula sheets hub.

Quick facts

Chapters
Light, human eye, electricity, magnetic effects
Most used
$V = IR$
Mirror formula
$\frac{1}{v} + \frac{1}{u} = \frac{1}{f}$
Lens formula
$\frac{1}{v} - \frac{1}{u} = \frac{1}{f}$
Energy unit
1 kWh = 3.6 × 10⁶ J
Sign rule
New Cartesian sign convention

Light: reflection by spherical mirrors

Mirror formulas
Formula	Used for	SI unit	Guide
$f = \frac{R}{2}$	focal length from radius of curvature	m	Mirror guide
$\frac{1}{v} + \frac{1}{u} = \frac{1}{f}$	locating the image formed by a curved mirror	m⁻¹	Mirror formula guide
$m = \frac{h'}{h} = -\frac{v}{u}$	how much bigger the image is	no unit	Mirror magnification guide

Example 1: a concave mirror

A small toy is set 24 cm from a concave mirror whose focal length is 16 cm. Where is the image, and how large is it?

Signs: u = −24 cm, f = −16 cm. Rearranging the mirror formula, $\frac{1}{v} = -\frac{1}{16} + \frac{1}{24} = \frac{-3 + 2}{48} = -\frac{1}{48}$ , so v = −48 cm.

$m = -\frac{v}{u} = -\frac{-48}{-24} = -2$ . Answer: a real, inverted image 48 cm in front of the mirror, twice the height of the toy.

Light: refraction, lenses and power

Refraction and lens formulas
Formula	Used for	SI unit	Guide
$n = \frac{c}{v}$	absolute refractive index	no unit	Refractive index guide
$n_{21} = \frac{\sin i}{\sin r}$	Snell's law for two media	no unit	Snell's law guide
$\frac{1}{v} - \frac{1}{u} = \frac{1}{f}$	finding where a thin lens puts the image	m⁻¹	Lens formula guide
$m = \frac{h'}{h} = \frac{v}{u}$	lens magnification	no unit	Lens magnification guide
$P = \frac{1}{f\,(\text{in m})}$	power of a lens	dioptre (D)	Power of lens guide
$P = P_1 + P_2 + \dots$	lenses in contact	D	Lens power guide

Convex lenses carry positive f and positive P; concave lenses carry negative values of both. In the human eye chapter, a short sighted (myopic) eye is corrected with a concave lens and a long sighted (hypermetropic) eye with a convex lens, and you find the power from P = 1/f. Notice that the mirror magnification has a minus sign and the lens one does not.

Class 10 physics all formulas PDF: electricity

Charge, current, resistance and power
Formula	Used for	SI unit	Guide
$Q = It$	charge passed in time t	C	Charge guide
$V = \frac{W}{Q}$	potential difference as work per charge	V	Voltage guide
$V = IR$	current through a resistor at fixed temperature	V	Ohm's law guide
$R = \rho\frac{l}{A}$	resistance of a wire	Ω	Resistivity guide
$R_s = R_1 + R_2 + \dots$	resistances joined end to end	Ω	Resistance guide
$\frac{1}{R_p} = \sum \frac{1}{R_i}$	resistances side by side	Ω	Resistors guide
$H = I^2Rt$	heat produced (Joule's law of heating)	J	Heat guide
$P = VI$	electric power, also written I²R or V²/R	W	Current guide

Example 2: a parallel pair and the energy bill

Resistors of 5 Ω and 20 Ω are joined in parallel across an 8.0 V supply. Find the total resistance, the current drawn and the power. Then find the energy, in kWh, used by a 1.5 kW heater running 3 hours a day for 30 days.

$\frac{1}{R_p} = \frac{1}{5} + \frac{1}{20} = \frac{5}{20}$ , so $R_p = 4.0\ \Omega$ . Current $I = \frac{8.0}{4.0} = 2.0\ \text{A}$ , power $P = (8.0)(2.0) = 16\ \text{W}$ .

Heater: $E = Pt = (1.5\ \text{kW})(3 \times 30\ \text{h}) = 135\ \text{kWh}$ , which is $135 \times 3.6 \times 10^6 = 4.86 \times 10^8\ \text{J}$ .

A parallel combination always comes out below its lowest resistor. A bigger answer means a slip in the reciprocal step.

Class 10 physics all chapter formula sheet: what has no formula

The magnetic effects chapter is mostly about field patterns, the right hand thumb rule, Fleming's left hand rule for the force on a conductor, and how electric motors and domestic circuits work. Learn those rules and diagrams; they score as well as any calculation. The colourful world part of the human eye chapter, on dispersion, scattering and the blue sky, is also descriptive. A useful number to remember is the least distance of distinct vision, about 25 cm for a normal eye.

Class 9 physics formulas for a quick look back

Class 9 motion, force, gravitation, work and sound
Formula	Used for	SI unit	Guide
$v^2 - u^2 = 2as$	third equation of motion, with v = u + at and its partner	m/s, m	Equations of motion guide
$F = ma,\ p = mv$	force and momentum	N, kg m/s	Momentum guide
$W = mg$	weight	N	Weight guide
$P = \frac{F}{A}$	pressure	Pa	Pressure guide
$\rho = \frac{m}{V}$	density	kg/m³	Density guide
$KE = \frac{1}{2}mv^2,\ PE = mgh$	energy of motion and of height	J	Kinetic energy guide
$v = f\lambda,\ 2d = vt$	speed of sound and echo distance	m/s, m	Speed of sound guide

Many of these return in Class 10 problems, especially work and power in the electricity chapter.

Revision tips and traps

Write the signs before you start. Object distance u is negative for both mirrors and lenses when the object is on the left.
Convert centimetres to metres for power. f = 25 cm gives P = 1/0.25 = 4 D, not 1/25.
Use the right resistance rule. Household appliances are wired in parallel so each gets the full voltage.
Keep kWh and J apart. The commercial unit of energy is 1 kWh = 3.6 × 10⁶ J.

Students heading on to Class 11 and Class 12 physics all chapter formula sheet pages can start with the links in the introduction. A Class 12 physics all formulas PDF copy is available the same way, by printing that page.

Frequently asked questions

How can I download this Class 10 physics formula list as a PDF?

Use your browser's print option and select save as PDF. The tables print neatly on standard pages.

What is the formula for the power of a lens?

Power equals one over the focal length measured in metres, P = 1/f, and its unit is the dioptre (D). A convex lens has positive power and a concave lens negative power.

What is the difference between the mirror formula and the lens formula?

For mirrors you add the reciprocals, 1/v + 1/u = 1/f. For lenses you subtract them, 1/v − 1/u = 1/f. Their magnification formulas also differ in sign: −v/u for mirrors and v/u for lenses.

What is the SI unit of resistance and resistivity?

Resistance is measured in ohms (Ω) and resistivity in ohm metres (Ω m). Resistivity depends on the material, while resistance also depends on length and area.

Which Class 10 physics chapter has the most numericals?

Electricity and light usually carry the most numerical questions. The magnetic effects chapter is mostly diagrams, rules and explanations.