Grade 10 electricity – D.C Electric Circuits Quiz
1. What is electric current in a D.C. circuit?
Electric current is defined as the rate at which electric charge flows past a point in a conductor, usually measured in amperes (A).
2. Which device is used to measure electric current in a circuit?
An ammeter measures current and must be connected in series so that the entire current flows through it; a voltmeter is connected in parallel.
3. What is the unit of electric potential difference (voltage)?
Voltage or potential difference is measured in volts (V). Ohm is resistance, ampere is current, watt is power.
4. Ohm's law relates which three quantities in a D.C. circuit?
Ohm's law states V = I × R, relating voltage (V), current (I) and resistance (R) in many conductors under constant conditions.
5. A 9 V battery is connected to a resistor of 3 Ω. What is the current through the resistor?
Using Ohm's law I = V/R = 9 V / 3 Ω = 3 A.
6. Two resistors of 4 Ω and 6 Ω are connected in series. What is their total resistance?
Resistances in series add: R_total = 4 Ω + 6 Ω = 10 Ω.
7. Two resistors of 4 Ω and 6 Ω are connected in parallel. What is their equivalent resistance?
Parallel resistance: 1/R = 1/4 + 1/6 = 5/12, so R = 12/5 = 2.4 Ω.
8. If identical 1.5 V cells are placed in series, what happens to the total voltage?
In series the EMFs add, so connecting cells in series raises the total voltage by summing each cell's voltage.
9. If identical 1.5 V cells are placed in parallel, what happens to the total voltage (neglecting internal resistance)?
Ideal identical cells in parallel keep the same terminal voltage as one cell but increase available current capacity.
10. What does a short circuit mean in a D.C. circuit?
A short circuit provides a near-zero resistance path across the supply, leading to very large currents that can cause damage or fire.
11. Which statement best describes an open circuit?
An open circuit has a discontinuity (break), preventing current from flowing through the circuit.
12. A voltmeter should be connected how when measuring the voltage across a resistor in a D.C. circuit?
A voltmeter measures potential difference across two points, so it must be connected in parallel with the component.
13. What is the correct direction of conventional current in a circuit?
Conventional current is defined as flow of positive charge from the positive to negative terminal; electron flow is opposite.
14. A resistor dissipates 6 W of power when 2 A flows through it. What is the voltage across the resistor?
Power P = V × I, so V = P/I = 6 W / 2 A = 3 V.
15. What is electrical resistance a measure of in a conductor?
Resistance quantifies how much a material resists current flow; higher resistance means less current for the same voltage.
16. Two bulbs are connected in series to a battery. If one bulb blows (filament breaks), what happens to the other bulb?
In series the same current flows through each component; if the circuit is broken by a blown bulb, current stops and all go out.
17. Which of the following best describes internal resistance of a cell?
Internal resistance is the cell's inherent resistance; when current flows, a voltage drop across it reduces the terminal voltage from the EMF.
18. A 12 V battery with internal resistance 1 Ω supplies current through an external resistor of 5 Ω. What is the terminal voltage across the external resistor?
Total resistance = 1 + 5 = 6 Ω, current = 12/6 = 2 A. Voltage across external resistor = I × 5 = 2 × 5 = 10 V.
19. Which quantity remains the same at every point in a series circuit?
In series circuits the same current flows through every component; voltages and powers may differ.
20. Which quantity is the same across each branch of a parallel circuit?
In parallel circuits each branch is connected across the same two points, so the voltage across each branch is the same.
21. A fuse is used in a D.C. electrical system to protect circuits. How does it protect the circuit?
A fuse has a thin wire that melts when excessive current passes, opening the circuit and preventing damage or fire.
22. What is electrical power in a circuit defined as?
Power is energy per unit time, often given by P = V × I, representing how fast electrical energy is used or delivered.
23. Two resistors of 8 Ω and 8 Ω are connected in parallel and then connected to a 12 V battery. What is the total current drawn from the battery?
Parallel equivalent is 4 Ω (since 1/R = 1/8 + 1/8 = 1/4), so I = V/R = 12/4 = 3 A.
24. Kirchhoff's junction rule (node rule) in D.C. circuits states which of the following?
Kirchhoff's junction rule expresses charge conservation: currents entering a node must equal currents leaving it.
25. In applying Kirchhoff's loop rule to a simple D.C. closed loop, what is the loop rule?
Kirchhoff's loop rule states that the sum of EMF and potential drops around any closed path is zero, reflecting energy conservation.
26. What happens to the total current drawn from a battery if you add another identical resistor in series to an existing series chain?
Adding a resistor in series raises overall resistance, and for the same battery voltage, current I = V/R decreases.
27. When performing experiments with D.C. circuits in a Kenyan school lab, which safety practice is most important?
Turning off power prevents accidental shocks, short circuits and damaged components; the other practices are unsafe.
28. What is an electric circuit?
An electric circuit is a continuous closed path composed of conductors and components that allows charge to move and produce current. Open paths or isolated batteries do not form circuits.
29. Which quantity measures the rate of flow of electric charge in a conductor?
Electric current is the rate of flow of charge and is measured in amperes (A). Voltage measures potential difference, resistance opposes current, and power is energy per time.
30. What is the conventional direction of current flow in circuit diagrams?
Conventional current is defined as flowing from positive to negative outside the battery. Electron flow is opposite, but circuit diagrams use conventional direction.
31. Ohm's law states a relationship between which three quantities?
Ohm's law relates voltage (V), current (I) and resistance (R) by V = I × R in ohmic conductors.
32. If a resistor has resistance 2 Ω and current 0.5 A flows through it, what is the voltage across it?
Using V = I × R: V = 0.5 A × 2 Ω = 1 V.
33. Which factor does NOT significantly affect the resistance of a uniform metal wire?
Resistance depends on length, cross-sectional area and material. The colour of the insulation does not affect the metal wire's resistance.
34. How do resistances add when connected in series?
In series connections, resistances add directly: R_total = R1 + R2 + ... because current passes through each resistor consecutively.
35. How is the equivalent resistance of two resistors connected in parallel calculated (R1 and R2)?
For parallel resistors the reciprocals add. The equivalent resistance is found from 1/R_eq = 1/R1 + 1/R2, giving a value smaller than the smallest resistor.
36. Which instrument should be connected in series with a component to measure the current flowing through it?
An ammeter measures current and must be placed in series so the circuit current flows through the meter. A voltmeter is connected in parallel.
37. Where should a voltmeter be connected to measure the potential difference across a resistor?
A voltmeter measures the potential difference between two points and must be connected in parallel across the component whose voltage is measured.
38. What happens in a short circuit?
A short circuit provides a low-resistance path that bypasses components, causing very high current that can damage components or cause fire.
39. What is the purpose of a fuse in a DC circuit at home?
A fuse contains a thin wire that melts under excessive current, opening the circuit and preventing overheating and fires.
40. How is electrical power delivered to a resistor calculated using voltage and current?
Electrical power (P) is the product of voltage (V) across a component and the current (I) through it: P = V × I, measured in watts (W).
41. Which unit is used to measure electrical charge?
Electric charge is measured in coulombs (C). Ohm is resistance, watt is power, and meter measures length.
42. What is the effect of connecting identical batteries in series?
Connecting cells in series adds their voltages while the charge capacity (ampere-hour) stays the same as a single cell.
43. What is electromotive force (EMF) of a cell?
EMF is the open-circuit voltage of a cell – the maximum potential difference between its terminals when no current is drawn.
44. Why does the terminal voltage of a battery drop when a heavy current is drawn?
Internal resistance inside the battery causes a voltage drop (I × r) when current flows, reducing the terminal voltage under heavy load.
45. In a simple series circuit with three resistors, what is true about the current through each resistor?
In series circuits the same current flows through every component because there is only one path for charge to move.
46. In a parallel circuit what happens to the brightness of a bulb if another identical bulb is added in a separate parallel branch (same supply)?
In parallel each branch gets the full supply voltage, so adding another identical branch does not significantly change voltage across each bulb; brightness remains about the same.
47. Which statement best describes resistance in terms of collision of electrons in a conductor?
As electrons move through a conductor they collide with atoms and impurities; these collisions impede flow and convert electrical energy into heat, which we call resistance.
48. How should you use an ohmmeter to measure the resistance of a resistor in a circuit?
Ohmmeters apply a small test current; to measure a single resistor accurately, the circuit must be unpowered and the resistor isolated to avoid parallel paths or damage to the meter.
49. What is Kirchhoff's current law (KCL) at a circuit junction?
KCL expresses conservation of charge: at any node (junction) the total incoming current equals total outgoing current.
50. What is the correct unit for electrical resistance?
Resistance is measured in ohms (Ω). Volt measures potential difference, ampere measures current, and joule measures energy.
51. A 12 V battery supplies 2 A to a circuit. What is the electrical power delivered by the battery?
Power P = V × I = 12 V × 2 A = 24 W.
52. Why are conductors like copper used for wiring in household DC circuits?
Copper and similar metals have low resistivity, so they conduct electricity efficiently with minimal energy loss as heat, making them ideal for wiring.
53. If two resistors of 6 Ω and 3 Ω are connected in series and the battery supplies 9 V, what current flows in the circuit?
Series total R = 6 + 3 = 9 Ω. Current I = V / R = 9 V / 9 Ω = 1 A.
54. A resistor dissipates 10 W of power when 2 A passes through it. What is the voltage across the resistor?
Power P = V × I, so V = P / I = 10 W / 2 A = 5 V.