Electricity – Very Short Answer Type Questions
60 Very Short Answer Questions — Electricity
CBSE Board Examination Focus:
- Clear, concise answers to score in short-answer sections.
- Important definitions, formulae and quick numerical tips.
- Topic-wise coverage for rapid revision.
Instructions: 60 very short answer questions with direct answers. Use these for quick recall and last-minute revision; practise writing similar short answers in examinations.
Very Short Answer Questions (1–60)
1. What is electric current?
Answer: Electric current is the rate of flow of charge; I = Q/t, unit ampere (A).
2. What is the SI unit of charge?
Answer: Coulomb (C).
3. Define potential difference.
Answer: Potential difference between two points is the work done per unit charge to move a charge between them; unit volt (V).
4. State Ohm's law.
Answer: For an ohmic conductor at constant temperature, V ∝ I, or V = IR.
5. What is resistance?
Answer: Resistance is the opposition a conductor offers to current; R = V/I, unit ohm (Ω).
6. Give the relation between resistance, length and area.
Answer: R = ρ (l/A), where ρ is resistivity, l length, A cross‑sectional area.
7. What is resistivity?
Answer: Resistivity (ρ) is a material property that quantifies how strongly a material opposes current; unit Ω·m.
8. How do resistances add in series?
Answer: In series, R_total = R_1 + R_2 + ⋯
9. How do resistances add in parallel?
Answer: In parallel, 1/R_total = 1/R_1 + 1/R_2 + ⋯
10. What is electric power?
Answer: Power is rate of energy conversion P = VI = I²R = V²/R, unit watt (W).
11. What does a voltmeter measure and how is it connected?
Answer: A voltmeter measures potential difference and is connected in parallel across the component.
12. What does an ammeter measure and how is it connected?
Answer: An ammeter measures current and is connected in series with the circuit element.
13. Define EMF.
Answer: Electromotive force (EMF) is energy supplied per unit charge by a source; unit volt (V).
14. What is internal resistance?
Answer: Internal resistance is the resistance within a cell that reduces terminal voltage when current flows.
15. Write the relation between EMF (E), terminal voltage (V) and internal resistance (r).
Answer: V = E − Ir (when current flows out of the cell).
16. What is a conductor?
Answer: A conductor allows easy flow of electric charge (e.g., metals) due to free electrons.
17. Give an example of an insulator.
Answer: Rubber, glass, or plastic — materials that do not allow free flow of charge.
18. What is a semiconductor? Give an example.
Answer: A material with conductivity between conductors and insulators; e.g., silicon, germanium.
19. What is a fuse and its purpose?
Answer: A fuse is a protective device that melts to break the circuit when current exceeds safe value, preventing damage/fire.
20. Why is earthing (grounding) important?
Answer: Earthing provides a low resistance path to divert fault currents safely to ground, protecting users from shock.
21. State Joule's law of heating.
Answer: Heat produced H = I²Rt in time t in a resistor R carrying current I.
22. What is the unit of electrical energy used in billing?
Answer: Kilowatt‑hour (kWh).
23. How many joules are there in 1 kWh?
Answer: 1 kWh = 3.6 × 10⁶ J.
24. What is meant by an ohmic conductor?
Answer: An ohmic conductor obeys Ohm's law; V–I graph is a straight line through origin.
25. Give one example of a non‑ohmic device.
Answer: A filament bulb or a diode (V–I relation not linear).
26. What happens to resistance of a metal wire if its length is doubled?
Answer: Resistance doubles (R ∝ l).
27. What happens to resistance if cross‑sectional area is doubled?
Answer: Resistance halves (R ∝ 1/A).
28. Define drift velocity.
Answer: Drift velocity is the average velocity of charge carriers under an electric field in a conductor.
29. What is the relation between current density J and drift velocity vd?
Answer: J = n e vd, where n is carrier density and e charge of electron.
30. What is meant by 'short circuit'?
Answer: Short circuit is an unintended low resistance path causing excessive current which can damage circuits/fire.
31. How does temperature affect resistance of a metal?
Answer: Resistance of metals generally increases with temperature due to increased lattice vibrations.
32. How does temperature affect resistance of a semiconductor?
Answer: Resistance of semiconductors decreases with temperature as more charge carriers are freed.
33. What is a potentiometer used for?
Answer: A potentiometer measures EMF accurately and compares potentials; can also act as variable resistor.
34. What is the function of a cell in a circuit?
Answer: A cell supplies energy to move charges around the circuit (provides EMF).
35. Define terminal voltage of a cell.
Answer: Terminal voltage is the potential difference across the cell's terminals; V = E − Ir (when current flows).
36. How is the equivalent resistance of two equal resistors R in parallel related to R?
Answer: R_eq = R/2.
37. What is Kirchhoff's current law (KCL)?
Answer: Sum of currents entering a junction equals sum leaving it (conservation of charge).
38. What is Kirchhoff's voltage law (KVL)?
Answer: Sum of potential differences around any closed loop equals zero (energy conservation).
39. What is the typical domestic voltage in India?
Answer: Approximately 230 V (single‑phase supply).
40. State one use of the heating effect of current.
Answer: Electric heaters, kettles, toasters, filament lamps use heating effect.
41. What is the relation between power, voltage and current?
Answer: P = VI.
42. How is energy related to power?
Answer: Energy E = P t (power multiplied by time).
43. Define electric circuit.
Answer: An electric circuit is a closed path that allows current to flow from a source through devices and back to source.
44. What is a cell rating E (EMF)?
Answer: EMF is maximum potential difference when no current is drawn (open‑circuit voltage).
45. What is the significance of a graph of V versus I for a resistor?
Answer: Slope gives resistance; linear graph indicates ohmic behaviour.
46. What is the formula for combining three resistances in series?
Answer: R_total = R_1 + R_2 + R_3.
47. What is the formula for combining three equal resistances R in parallel?
Answer: R_eq = R/3.
48. What safety device is used to protect against overcurrent in circuits?
Answer: Fuse or circuit breaker.
49. What is a load in an electric circuit?
Answer: A device that consumes electrical energy (e.g., bulb, motor) is a load.
50. What is meant by 'rating' of an electrical appliance?
Answer: Rating is the power and voltage at which an appliance is designed to operate (e.g., 60 W, 230 V).
51. What is the effect of connecting resistors in parallel on total current drawn from source?
Answer: Total current increases because equivalent resistance decreases.
52. In which direction do electrons flow in a circuit relative to conventional current?
Answer: Electrons flow opposite to the direction of conventional current.
53. What is the charge of one electron?
Answer: Approximately −1.6 × 10⁻¹⁹ coulomb.
54. How is resistance affected if the material's resistivity doubles?
Answer: Resistance doubles (R ∝ ρ).
55. What is the purpose of a rheostat?
Answer: A rheostat is a variable resistor used to control current in a circuit.
56. What is an ammeter's ideal internal resistance?
Answer: Ideally zero (to avoid dropping voltage and altering current measurement).
57. What is a voltmeter's ideal internal resistance?
Answer: Ideally infinite (to avoid drawing current from the circuit).
58. What does a negative slope in V–I graph indicate for an element?
Answer: It indicates non‑ohmic behaviour where resistance changes with voltage/current (e.g., negative differential resistance).
59. Give one real-life example of series connection usage.
Answer: Old decorative string lights connected in series (if one bulb blows, whole string goes off).
60. Give one real-life example of parallel connection usage.
Answer: Domestic household wiring — appliances are connected in parallel so each gets full voltage.