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.