Grade 10 physics – Current Electricity Quiz
1. What is electric current?
Electric current is defined as the rate of flow of electric charge (usually electrons in a metal) past a point in a circuit.
2. What is the SI unit of electric current?
The ampere (A) is the SI unit of electric current; one ampere is one coulomb of charge passing a point per second.
3. Which symbol is commonly used for electric current in circuit equations?
The symbol I is used to represent electric current in circuit equations (from the French intensité de courant).
4. Ohm's law relates voltage (V), current (I) and resistance (R). Which equation is Ohm's law?
Ohm's law states that the potential difference V across a conductor is proportional to the current I through it, with resistance R as the constant: V = I × R.
5. What is the unit of electrical resistance?
The ohm (Ω) is the SI unit of resistance, defined by V = I × R.
6. If you add another resistor in series to a simple circuit with the same battery, what happens to the current?
Adding resistance in series increases the total resistance, so for the same battery emf the current (I = V/RT) decreases.
7. How does the total resistance of resistors connected in parallel compare to the smallest individual resistance?
For resistors in parallel the combined resistance is given by 1/RT = 1/R1 + 1/R2 + ...; this results in RT being less than the smallest branch resistance.
8. Where should an ammeter be connected when measuring current in a circuit?
An ammeter must be placed in series so the same current flows through it; connecting it in parallel could short the circuit.
9. Where should a voltmeter be connected when measuring the potential difference across a component?
A voltmeter measures potential difference between two points and must be connected in parallel across the component so it measures the correct voltage.
10. In a series circuit containing several resistors, which quantity is the same through each resistor?
In a series circuit the same current flows through all components because there is only one path for charge to move.
11. In a parallel circuit, which quantity is the same across each branch?
In a parallel circuit each branch is connected directly across the supply, so the potential difference (voltage) across every branch is the same.
12. What mainly causes electrical resistance in a metal conductor?
Resistance arises as moving electrons collide with vibrating atoms/ions in the metal lattice, converting electrical energy into heat.
13. A 12 V battery is connected to a resistor of 4 Ω. What is the current in the circuit?
Use I = V/R = 12 V / 4 Ω = 3 A.
14. A device has a potential difference of 6 V across it and carries a current of 2 A. What is the electrical power used?
Power P = V × I = 6 V × 2 A = 12 W.
15. Two identical 1.5 V cells are connected in series. What is the total emf of the combination?
Emfs in series add: 1.5 V + 1.5 V = 3.0 V.
16. When a current flows through a real battery, the terminal voltage is usually less than the emf. Why?
Internal resistance in the cell causes a voltage drop equal to Ir_internal when current flows, making terminal voltage V = emf − Ir_internal.
17. Which of these materials is a good electrical conductor commonly used in wiring?
Copper has many free electrons and low resistance, so it is widely used for electrical wiring.
18. What is the role of a battery (cell) in a circuit?
A battery converts chemical energy into electrical energy, doing work on charges so they can move through the circuit.
19. An ideal ammeter should have what kind of resistance to avoid changing the circuit current?
An ammeter must have very low resistance so it does not add significant resistance to the circuit and alter the current being measured.
20. An ideal voltmeter should have what kind of resistance when measuring voltage across a component?
A voltmeter must have a very high resistance to draw negligible current so it does not change the voltage it is intended to measure.
21. How do you find the total resistance of resistors connected in series R1 and R2?
Resistances in series add directly: the total resistance is the sum of individual resistances.
22. If the resistance in a circuit is doubled while the voltage remains the same, what happens to the current?
Using I = V/R, if R doubles and V is constant, I becomes half its original value.
23. Conventional current direction is defined as the direction positive charges would move. Which way is conventional current in a simple cell circuit?
By convention current direction is from positive to negative outside the cell, even though electrons actually flow the opposite way.
24. A 100 W lamp is switched on for 5 hours. How much electrical energy does it use in kilowatt-hours (kWh)?
Energy (kWh) = Power (kW) × time (h). 100 W = 0.1 kW; 0.1 kW × 5 h = 0.5 kWh.
25. Which expression gives the heat energy produced (Joule heating) in a resistor carrying current I for time t?
Joule's law states heat energy produced is Q = I^2 R t, where I is current, R resistance and t time.