Electricity
Subject: General Science
Sample Practice Questions
Question 1: What is the SI unit of electric current?
- Volt
- Ohm
- Ampere
- Coulomb
Explanation: The SI unit of electric current is the ampere (A). One ampere is constituted by the flow of one coulomb of charge per second (1 A = 1 C/s).
Question 2: How is potential difference (V) related to work done (W) and charge (Q)?
- V = W × Q
- V = W/Q
- V = Q/W
- V = W + Q
Explanation: Potential difference is defined as the work done to move a unit charge from one point to another. V = W/Q, where V is potential difference, W is work done, and Q is charge.
Question 3: What does Ohm's law state?
- V is inversely proportional to I
- V is directly proportional to I at constant temperature
- I is directly proportional to R
- V is directly proportional to R at constant temperature
Explanation: Ohm's law states that the potential difference across the ends of a metallic wire is directly proportional to the current flowing through it, provided its temperature remains the same. Mathematically, V ∝ I or V/I = R.
Question 4: What is the equivalent resistance when three resistors of 6 Ω each are connected to get 9 Ω?
- Two in parallel, one in series
- All in series
- All in parallel
- Two in series, one in parallel
Explanation: To get 9 Ω, connect two 6 Ω resistors in parallel (equivalent = 3 Ω) and then connect the third 6 Ω resistor in series. Total = 3 + 6 = 9 Ω.
Question 5: What is the conventional direction of electric current?
- Same as the direction of electron flow
- Opposite to the direction of electron flow
- Flow of positive charges
- Both B and C
Explanation: Conventionally, electric current is considered to be the flow of positive charges. Since electrons are negatively charged, the direction of electric current is taken as opposite to the direction of electron flow.
Question 6: Which material is the best conductor of electricity?
- Copper
- Aluminium
- Silver
- Gold
Explanation: According to Table 11.2, silver has the lowest resistivity (1.60 × 10^-8 Ω m), making it the best conductor of electricity. Copper is the second best.
Question 7: What is the SI unit of electric power?
- Joule
- Watt
- Volt-ampere
- Kilowatt-hour
Explanation: The SI unit of electric power is the watt (W). One watt is the power consumed by a device that carries 1 A of current when operated at a potential difference of 1 V.
Question 8: What is the relationship between current (I) and charge (Q) flowing through a conductor?
- I = Q × t
- I = Q/t
- I = t/Q
- I = Q + t
Explanation: Electric current is the rate of flow of electric charge. Mathematically, I = Q/t, where I is current, Q is charge, and t is time.
Question 9: What factors does the resistance of a conductor depend on?
- Length only
- Area of cross-section only
- Length, area of cross-section, and material
- Temperature only
Explanation: The resistance of a conductor depends on its length (directly proportional), its area of cross-section (inversely proportional), and the nature of its material. It also varies with temperature.
Question 10: Why are alloys used in electrical heating devices?
- They have low resistivity
- They do not oxidise readily at high temperatures
- They are cheaper than pure metals
- They have low melting points
Explanation: Alloys do not oxidise (burn) readily at high temperatures. For this reason, they are commonly used in electrical heating devices like electric irons, toasters, etc.