All Formula of Electricity Class 10

Electricity and magnetism formulasClass 10Class 12Updated 1 Nov 2026

V = IR

where

V potential difference V
I current A
R resistance Ω

Here is all formula of electricity class 10 students need, in the order the chapter builds them: charge and current, potential difference, Ohm's law $V = IR$ , resistance and resistivity, resistors in series and parallel, then electric power and the heating effect. Each one comes with a line on what it means, its unit, and where to go for solved problems on it.

The same ideas carry straight on into Class 12 and AP Physics, where you add electric fields, capacitors, drift velocity and magnetism. The second half of this hub lists those formulas too, so you can see where the Class 10 basics lead. If you only have an evening before a test, learn the first table and the exam traps section.

All formula of electricity class 10: V = I R

Quick facts

Core law
$V = IR$ (Ohm's law)
Current
$I = \frac{Q}{t}$
Resistance of a wire
$R = \frac{\rho L}{A}$
Power
$P = VI = I^2R = \frac{V^2}{R}$
Heating
$H = I^2Rt$
Commercial energy unit
1 kW h = 3.6 × 10⁶ J
Charge on an electron
1.602 × 10⁻¹⁹ C

How the electricity formulas fit together

Think of the chapter as one chain. Charge flowing per second is current. Energy given to each coulomb is potential difference. The ratio of the two is resistance, and the material and shape of a wire decide how big that ratio is. Multiply voltage by current and you get power, the energy used each second. Multiply power by time and you get the energy that shows up on an electricity meter or as heat in a wire.

So almost every numerical question in the chapter is a two step problem: use Ohm's law to find the missing one of V, I and R, then use a power or heat formula. Spot which link of the chain the question starts from and the route becomes clear.

All formula of electricity class 10 in one table

Class 10 electricity formulas with units
Quantity	Formula	Unit	Read more
Electric current	$I = \frac{Q}{t}$	ampere (A)	Current
Charge from electrons	$Q = ne$	coulomb (C)	Charge
Potential difference	$V = \frac{W}{Q}$	volt (V)	Voltage
Ohm's law	$V = IR$	V, A, Ω	Ohm's law
Resistance	$R = \frac{V}{I}$	ohm (Ω)	Resistance
Resistivity	$\rho = \frac{RA}{L}$	Ω m	Resistivity
Series resistors	$R_s = R_1 + R_2 + R_3$	Ω	Combinations
Parallel resistors	$\frac{1}{R_p} = \frac{1}{R_1} + \frac{1}{R_2} + \frac{1}{R_3}$	Ω	Combinations
Electric power	$P = VI = I^2R = \frac{V^2}{R}$	watt (W)	Below
Heat produced	$H = I^2Rt$	joule (J)	Heat
Electrical energy	$E = Pt$	J or kW h	Energy

1 kW h = 1000 W × 3600 s = 3.6 × 10⁶ J. This is the unit printed on household meter readings.

Series and parallel in practice

In a series circuit the same current flows through every resistor, and the voltages add up to the supply voltage. In parallel, every branch gets the full supply voltage, and the branch currents add up to the total. Household wiring is parallel so that each appliance gets the full mains voltage and can be switched on or off without affecting the others.

Example: a mixed circuit

Resistors of 4 Ω and 12 Ω are connected in parallel, and this pair is in series with a 2 Ω resistor across a 10 V battery. Find the current from the battery.

$\frac{1}{R_p} = \frac{1}{4} + \frac{1}{12} = \frac{1}{3} \Rightarrow R_p = 3\ \Omega$

Total resistance = 3 + 2 = 5 Ω.

$I = \frac{V}{R} = \frac{10}{5} = 2.0\ \text{A}$

The voltage across the parallel pair is 2.0 × 3 = 6.0 V, so 1.5 A goes through the 4 Ω branch and 0.5 A through the 12 Ω branch.

Power, energy and heating

Electric power is the rate at which energy is transferred. Any of the three forms works, so pick the one that uses the values you are given: VI when you know both, I²R when current is known, V²/R when the voltage is fixed, as with mains appliances. A heater has a low resistance on purpose, because at fixed voltage a smaller R gives a larger V²/R.

Example: an appliance rating

A heater is rated 1000 W at 220 V. Find its current, its resistance and the energy it uses in 3 hours.

$I = \frac{P}{V} = \frac{1000}{220} \approx 4.5\ \text{A}, \qquad R = \frac{V^2}{P} = \frac{220^2}{1000} \approx 48\ \Omega$

Energy = 1.0 kW × 3 h = 3.0 kW h = 1.08 × 10⁷ J.

The heat produced in a conductor, H = I²Rt, is used in electric irons, toasters, bulbs and fuses. A fuse wire has a low melting point so that a large current melts it before it can damage the wiring.

Beyond Class 10: formulas of electricity in physics for Class 12

Once you move to Class 12, JEE, NEET or AP Physics 2, electricity widens into electrostatics, current at the scale of electrons, and magnetism. These pages carry the story on:

Next level electricity and magnetism formulas
Topic	Main formula	Page
Force between charges	$F = \frac{kq_1q_2}{r^2}$	Electrostatic force
Electric field	$E = \frac{F}{q}$	Electric field
Charge densities	$\lambda = \frac{q}{L},\ \sigma = \frac{q}{A},\ \rho = \frac{q}{V}$	Charge density
Capacitance	$C = \frac{Q}{V}$	Capacitance
Field energy	$u = \frac{1}{2}\varepsilon_0E^2$	Energy density
Drift of electrons	$v_d = \frac{I}{neA}$	Drift velocity
Current per area	$J = \frac{I}{A}$	Current density
Cell emf	$V = \varepsilon - Ir$	Electromotive force
Field of a wire	$B = \frac{\mu_0I}{2\pi r}$	Magnetic field
Force on a current	$F = BIL\sin\theta$	Magnetic force
Coil as a magnet	$m = NIA$	Magnetic moment
Flux per area	$B = \frac{\Phi}{A}$	Magnetic flux density

For the whole Class 10 syllabus across all chapters, see the Class 10 physics formulas page.

Study tips for the chapter

Learn the three quantities V, I and R together with their units and meters: voltmeter in parallel, ammeter in series.
Write the given values with units before choosing a formula. The units often tell you which formula to use.
For combination circuits, reduce parallel groups first, then add series parts, and redraw the circuit after each step.
Practise ratio questions such as what happens to R when a wire is stretched to double its length. They are quick marks.
Memorise that one kilowatt hour is 3.6 × 10⁶ J and that e = 1.602 × 10⁻¹⁹ C. Both appear often in numericals.

Exam traps in electricity numericals

Parallel answers bigger than the smallest resistor. That is impossible; recheck your reciprocals and remember to flip 1/R at the end.
Units of area. In R = ρL/A, mm² must become 10⁻⁶ m².
Diameter versus radius. Doubling the diameter makes the area four times larger.
Power of two bulbs. In series, the bulb with the higher resistance glows brighter, because I²R is larger for it. In parallel, the lower resistance bulb glows brighter, because V²/R is larger.
Energy units. Convert watts to kilowatts and seconds to hours before giving an answer in kW h.

Current is not used up in a circuit. The same current enters and leaves each resistor; what is transferred is energy.

Frequently asked questions

What are all the formulas of electricity class 10?

I = Q/t, V = W/Q, V = IR, R = ρL/A, series R = R₁ + R₂ + …, parallel 1/R = 1/R₁ + 1/R₂ + …, P = VI = I²R = V²/R, H = I²Rt and E = Pt.

What is the most important formula of electricity?

Ohm's law, V = IR. Almost every circuit numerical uses it at least once, usually together with a power formula.

What is the formula of electricity in physics for power?

P = VI. Using Ohm's law it can also be written as P = I²R or P = V²/R.

How do I remember the series and parallel formulas?

Series resistors simply add. Parallel resistors add as reciprocals, and the combined value always comes out below the lowest individual resistance.

What is 1 kilowatt hour in joules?

1 kW h = 1000 W × 3600 s = 3.6 × 10⁶ J.

Which formula gives the heat produced by a current?

Joule's law of heating, H = I²Rt, which can also be written VIt or V²t/R.

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