Class 10 Science: Electricity important questions

Electricity is a chapter of Class 10 Science for the Andhra Pradesh State Board. These 16 questions are marked Very Important, Important or Practice, and each answer has been checked by our team. Use them to revise, not as a prediction of what will come in the exam.

1. Practice · 1 marks

   1. Draw the symbol of an electric cell.

   Two parallel vertical lines: a longer thin line (the positive terminal) and a shorter thick line (the negative terminal).

2. Practice · 1 marks

   2. What is the SI unit of resistance?

   The ohm (Ω).

3. Important · 2 marks

   3. Pose any two questions to understand Ohm's law.

   1) "If the potential difference across a wire is doubled at constant temperature, what happens to the current?" (It doubles: I ∝ V.) 2) "For a given wire at constant temperature, does the ratio V/I stay the same?" (Yes: V/I = R, its resistance.)

4. Very Important · 8 marks

   4. Deduce the expression for the equivalent resistance of three resistors connected in parallel.

   Connect R₁, R₂ and R₃ in parallel across a battery of potential difference V. Each resistor has the same potential difference V. The total current divides: I = I₁ + I₂ + I₃. By Ohm's law, I₁ = V/R₁, I₂ = V/R₂, I₃ = V/R₃. If Rp is the equivalent resistance, I = V/Rp. So V/Rp = V/R₁ + V/R₂ + V/R₃, and dividing by V: 1/Rp = 1/R₁ + 1/R₂ + 1/R₃.

5. Important · 4 marks

   5. Write the advantages of parallel and series connections in daily life.

   Parallel: 1) Each appliance gets the full supply voltage. 2) Each appliance can be switched on or off independently, and if one fails the others keep working. 3) Each appliance draws only the current it needs. So houses are wired in parallel. Series: 1) The same current flows through every component, which is useful for fuses (a fuse is placed in series with the appliance it protects). 2) Small bulbs in decorative lighting can share a higher voltage. 3) A single switch controls the whole circuit.

6. Practice · 1 marks

   6. Resistors of 2 Ω and 4 Ω are connected in series. What is the resultant resistance?

   Rs = 2 + 4 = 6 Ω.

7. Important · 2 marks

   7. Why is series arrangement not used in domestic circuits?

   1) In series, if one appliance fails or is switched off, the circuit breaks and every appliance stops working. 2) The same current flows through all appliances, but different appliances need different currents. 3) The total resistance becomes large, so the current is small. In parallel, each appliance gets the full voltage and can be switched on or off independently.

8. Practice · 1 marks

   8. Draw the symbol of an ammeter.

   A circle with the letter A inside it, connected in the circuit line, with + and − marked on its terminals.

9. Practice · 1 marks

   9. Which device protects electric appliances from overloading in household circuits?

   An electric fuse (or a miniature circuit breaker, MCB).

10. Practice · 1 marks

    10. You have resistors of 6 Ω and 12 Ω. How do you connect them to get 4 Ω?

    Connect them in parallel: 1/R = 1/6 + 1/12 = 3/12 = 1/4, so R = 4 Ω.

11. Practice · 1 marks

    11. Why are alloys commonly used in electrical heating devices?

    Alloys such as nichrome have a higher resistivity than pure metals and do not oxidise (burn) easily at high temperatures, so they produce a lot of heat and last long.

12. Important · 2 marks

    12. Design a circuit with a battery, two resistors, a plug key and an ammeter, all connected in series.

    Connect everything in one loop: positive terminal of the battery → plug key → resistor R₁ → resistor R₂ → ammeter → negative terminal of the battery. The ammeter is in series, with its + terminal towards the battery's + terminal. The same current flows through every part of the circuit.

13. Very Important · 8 marks

    13. Define 1) electric current 2) potential difference 3) Ohm's law 4) electric power

    1) Electric current is the rate of flow of charge: I = Q/t. SI unit: ampere (A). 2) Potential difference between two points is the work done to move a unit charge from one point to the other: V = W/Q. SI unit: volt (V). 3) Ohm's law: at constant temperature, the current through a conductor is directly proportional to the potential difference across it: V = IR. 4) Electric power is the rate of consumption of electrical energy: P = W/t = VI = I²R = V²/R. SI unit: watt (W).

14. Practice · 1 marks

    14. Why are electric bulbs filled with nitrogen and argon?

    These gases are chemically inactive. They stop the hot tungsten filament from oxidising (burning) and so make the filament last longer.

15. Important · 2 marks

    15. A student needs to change the current in a circuit without changing the battery. Suggest a method and justify it.

    Connect a rheostat (variable resistor) in series. By Ohm's law I = V/R: with the battery voltage fixed, increasing the resistance decreases the current, and decreasing it increases the current.

16. Very Important · 8 marks

    16. Derive the equation Rs = R₁ + R₂ + R₃ for resistors in series.

    Connect R₁, R₂ and R₃ in series with a battery of potential difference V. The same current I flows through each resistor. The total potential difference is the sum of the potential differences across each: V = V₁ + V₂ + V₃. By Ohm's law, V₁ = IR₁, V₂ = IR₂, V₃ = IR₃. If Rs is the equivalent resistance, V = IRs. So IRs = IR₁ + IR₂ + IR₃, and dividing by I: Rs = R₁ + R₂ + R₃.