Class 10 Physics: Current, Voltage and Resistance Explained with Practice

Current, potential difference and resistance describe different features of a circuit. A student may remember V = IR yet still confuse what an ammeter measures or where a voltmeter belongs. This lesson joins the definitions to simple circuit reasoning, then uses worked calculations to check understanding.

Use the examples as focused revision rather than as a predicted paper. They assume ordinary school-level direct-current circuits and ideal connecting wires unless a question says otherwise.

Independent topic practice for Class 10 students. Check your textbook, examination scheme and assigned learning outcomes against the official FBISE assessment frameworks and model papers. These are original exercises, not an official answer key or a predicted examination paper.

What you will practise

• Separate the three quantities
• Understand the condition in Ohm’s law
• Connect meters correctly
• Compare series and parallel arrangements
• Calculate power after solving the circuit

Separate the three quantities

Current is the rate of flow of charge: I = Q/t. One ampere means one coulomb passes a point each second. Potential difference is energy transferred per unit charge: V = W/Q. One volt means one joule per coulomb. Resistance is the ratio V/I for the stated operating conditions.

Current is not a supply of energy that gets used up as it passes through a resistor. In a single steady series path, the current is the same at every point. Electrical energy is transferred in components, while charge continues around the complete circuit.

Understand the condition in Ohm’s law

Ohm’s law states that current is proportional to potential difference for a conductor when temperature and other relevant physical conditions remain constant. This condition belongs in a complete definition. The equation V = IR alone does not prove that a component is ohmic over every range.

For an ohmic resistor, a graph of V on the vertical axis against I on the horizontal axis is a straight line through the origin; its gradient is resistance. If the axes are reversed, the gradient is 1/R. Always inspect the axes before naming a gradient.

Connect meters correctly

An ammeter is connected in series with the component whose current is measured. Its resistance should be very low so it changes the circuit current as little as possible. A voltmeter is connected in parallel across a component and should have very high resistance.

Draw a circuit before placing the meters. A parallel voltmeter must touch the two ends of the same component. In practical work, follow your teacher’s setup and use only appropriate low-voltage school equipment. Never copy classroom circuit experiments onto a household supply.

Compare series and parallel arrangements

For resistors in series, Rtotal = R₁ + R₂ + … . The current is common to all resistors and the supply potential difference is shared. Adding another resistor in series increases the total resistance if all existing values stay the same.

For parallel resistors, 1/Rtotal = 1/R₁ + 1/R₂ + … . The potential difference across each branch is the same. Current divides between branches, with a larger current through a smaller resistance at the same voltage. The equivalent resistance is smaller than the smallest branch resistance.

Calculate power after solving the circuit

Electrical power is P = VI. For a resistor, substituting Ohm’s law also gives P = I²R and P = V²/R. Choose a form using quantities that belong to the same component. A supply voltage cannot be assigned to one resistor in a series chain without first finding its share.

Electrical energy transferred over a time t is E = Pt when power stays constant. Use seconds for joules and watts. A kilowatt-hour is an energy unit: 1 kWh = 3.6 × 10^6 J. It is not a unit of power.

Worked examples and model answers

1. Charge flow

A charge of 24 C passes in 6 s. Find current.

I = Q/t = 24/6 = 4 A. The meaning is 4 C per second.

2. Series circuit

Two resistors, 2 Ω and 4 Ω, are in series across 12 V.

Rtotal = 6 Ω; I = 12/6 = 2 A. The voltage drops are 4 V and 8 V, adding to 12 V.

3. Parallel circuit

A 6 Ω and a 3 Ω resistor are in parallel across 6 V.

Branch currents are 1 A and 2 A. Total current is 3 A, so Rtotal = 6/3 = 2 Ω. Total power is 18 W.

Practice MCQs

Attempt all six before opening the answers. Write a reason beside each choice so that a correct guess is not mistaken for understanding.

1. The SI unit of current is:

1. volt
2. ampere
3. ohm
4. joule

Answer and explanation

B. ampere An ampere is a coulomb per second.

2. A voltmeter is connected:

1. in series
2. in parallel
3. without a circuit
4. only across a wire

Answer and explanation

B. in parallel It compares potential at two points.

3. Two 5 Ω resistors in series give:

1. 2.5 Ω
2. 5 Ω
3. 10 Ω
4. 25 Ω

Answer and explanation

C. 10 Ω Series resistances add.

4. Across parallel branches, the common quantity is:

1. resistance always
2. current always
3. potential difference
4. power always

Answer and explanation

C. potential difference Each branch connects to the same two nodes.

5. A 2 A current through 3 Ω requires:

1. 1.5 V
2. 5 V
3. 6 V
4. 9 V

Answer and explanation

C. 6 V V = IR = 2 × 3.

6. A kilowatt-hour measures:

1. power
2. charge
3. energy
4. resistance

Answer and explanation

C. energy It is power multiplied by time.

Written self-check

1. Find the resistance of a component carrying 0.5 A at 6 V.
2. Find the power of a 12 V lamp carrying 0.25 A.
3. Find the equivalent resistance of two 8 Ω resistors in parallel.
4. Explain why a series circuit has the same current throughout.

Suggested answers

1. R = 12 Ω.
2. P = 3 W.
3. Rtotal = 4 Ω.
4. There is one steady path, with no charge accumulation at a component.

Use your mistakes to choose the next task

Mark the MCQs only after completing the written self-check. If you chose the correct answer but cannot explain it, return to the relevant heading and write a two-sentence explanation in your own words. If a calculation went wrong, identify whether the problem came from the starting relationship, the substitution, the arithmetic or the unit. That gives you a specific correction to practise.

On your next attempt, change the order of the questions and keep the answers covered. Explain one idea aloud, then answer one question on paper without consulting the notes. A successful immediate retry is useful, but a second correct attempt on a different day gives better evidence that you can recall and apply the idea independently.

Further study

Use the official FBISE framework and model-paper page to select the subject, level and scheme that apply to you. Match the learning outcomes with your assigned textbook before deciding how much detail to revise.

More practice on this blog: Earlier Physics MCQ practice.