Preparing for the TNPSC exam becomes easier with regular practice. This Physics Electricity Test 4 is designed to help you revise important Electricity concepts commonly asked in TNPSC Physics questions. Attempt these carefully selected MCQs, check your answers with explanations, and strengthen your understanding to improve your confidence for the TNPSC exam.
TNPSC Physics Electricity Test 4 – Detailed Explanations
This Electricity Test 4 covers important TNPSC General Science topics, including series and parallel circuits, electric power, electrical energy, Joule’s law of heating, household wiring, live, neutral and earth wires, fuse, MCB, short circuits, overloading, electrical safety, and practical applications of electricity. Practice these concept-based MCQs to strengthen your understanding, improve your problem-solving skills, and boost your confidence for the TNPSC exam.
1. In a parallel circuit, the potential difference across each branch is:
Answer: B. Equal to the supply voltage
In a parallel circuit, every branch is connected directly across the power source. Therefore, the potential difference (voltage) across each branch remains equal to the supply voltage, regardless of the number of branches.
Quick Revision:
- Voltage is the same across all branches in a parallel circuit.
- Current is divided among the branches.
Real-Life Example:
The lights and fans in a house are connected in parallel, so each appliance receives the full supply voltage independently.
2. Which law states that the heat produced in a conductor is directly proportional to the square of the current?
Answer: C. Joule’s Law of Heating
Joule’s Law of Heating states that the heat produced in a conductor depends on the square of the electric current, the resistance of the conductor, and the time for which the current flows. It is expressed by the formula H = I²Rt, where H is heat energy, I is current, R is resistance, and t is time. This principle explains why electrical appliances with heating elements generate heat when current passes through them.
Quick Revision:
- Heat produced ∝ Current² × Resistance × Time
- Formula: H = I²Rt
- Greater current produces much more heat.
Real-Life Example:
Electric irons, electric heaters, and electric kettles work based on Joule’s Law of Heating.
3. The commercial unit of electrical energy is:
Answer: C. Kilowatt-hour (kWh)
The commercial unit of electrical energy is the kilowatt-hour (kWh). It represents the amount of energy consumed when a 1000-watt appliance operates for one hour. Electricity consumption in homes and industries is measured in kilowatt-hours for billing purposes.
Quick Revision:
- Commercial unit of electrical energy = Kilowatt-hour (kWh)
- 1 kWh = 1 unit of electricity
- Used for electricity billing
Real-Life Example:
If a 1000 W electric heater runs for one hour, it consumes 1 kWh (1 unit) of electricity.
4. Which wire in domestic wiring carries electric current from the power supply to an appliance?
Answer: D. Live wire
The live wire carries electric current from the mains power supply to an electrical appliance. It is at a high electrical potential and is responsible for supplying electrical energy to the device. In domestic wiring, the live wire should always be handled carefully because it can cause electric shock if touched.
Quick Revision:
- Live wire carries current from the power supply.
- It is at high electrical potential.
- Usually identified by red or brown insulation.
Real-Life Example:
When you switch on a ceiling fan or light, the live wire supplies electricity from the mains to the appliance.
5. The main purpose of a fuse is to:
Answer: B. Prevent excessive current from damaging the circuit
A fuse is a safety device designed to protect electrical circuits and appliances from excessive current caused by overloading or a short circuit. It contains a thin metal wire that melts when the current exceeds the safe limit, automatically breaking the circuit and preventing damage.
Quick Revision:
- Fuse protects against excessive current.
- Melts when current exceeds the safe limit.
- Prevents damage to electrical appliances.
Real-Life Example:
If a short circuit occurs in your home, the fuse blows to disconnect the power supply and protect the wiring.
6. An MCB differs from a fuse because it:
Answer: A. Can be reset after tripping
A Miniature Circuit Breaker (MCB) is an automatic protective device that disconnects the electrical supply during an overload or short circuit. Unlike a fuse, an MCB does not melt and can be reset after the fault has been corrected, making it more convenient and reliable.
Quick Revision:
- MCB trips automatically during faults.
- Can be reset and reused.
- Provides better protection than a traditional fuse.
Real-Life Example:
Modern houses use MCBs in the distribution board, allowing power to be restored simply by resetting the switch after removing the fault.
7. Overloading in an electric circuit occurs when:
Answer: A. Too many appliances are connected to one circuit
Overloading occurs when the total current drawn by electrical appliances connected to a circuit exceeds its safe carrying capacity. This causes the wires to overheat, increasing the risk of damage to appliances and electrical fires.
Quick Revision:
- Too many appliances increase current.
- Excess current causes overheating.
- Overloading is prevented using fuses or MCBs.
Real-Life Example:
Connecting an electric heater, iron, and kettle to the same extension board at the same time may overload the circuit.
8. Which wire is usually connected to the metal body of an electrical appliance?
Answer: C. Earth wire
The earth wire is connected to the metal body of an electrical appliance to provide a safe path for leakage current to flow into the ground. This prevents the metal body from becoming electrically charged and protects users from electric shock.
Quick Revision:
- Earth wire provides safety.
- Carries leakage current safely to the ground.
- Prevents electric shock.
Real-Life Example:
The metal body of a refrigerator or washing machine is connected to the earth wire for user safety.
9. Which of the following appliances mainly works on the heating effect of electric current?
Answer: B. Electric iron
An electric iron works on the heating effect of electric current. When current flows through its high-resistance heating element, electrical energy is converted into heat energy, which is used to remove wrinkles from clothes.
Quick Revision:
- Electric iron uses the heating effect of current.
- Converts electrical energy into heat.
- Contains a high-resistance heating element.
Real-Life Example:
Electric irons are commonly used in homes to press clothes using the heat produced by the heating element.
10. Which of the following conditions is most likely to cause a short circuit?
Answer: B. Live and neutral wires coming into direct contact
A short circuit occurs when the live wire and neutral wire come into direct contact, creating a very low-resistance path. This allows a large amount of current to flow suddenly, which can damage electrical appliances, overheat wires, and increase the risk of fire.
Quick Revision:
- Live and neutral wires touching cause a short circuit.
- Very low resistance allows excessive current.
- Fuses and MCBs protect against short circuits.
Real-Life Example:
Damaged insulation on household wiring can cause the live and neutral wires to touch, resulting in a short circuit.
11. The SI unit of electric power is:
Answer: B. Watt
The SI unit of electric power is the watt (W), named after the Scottish engineer James Watt. Electric power is the rate at which electrical energy is converted or consumed in a circuit. One watt is equal to one joule of energy used per second.
Quick Revision:
- SI unit of electric power = Watt (W)
- 1 W = 1 joule/second
- Power indicates how quickly electrical energy is used.
Real-Life Example:
A 60 W LED bulb consumes electrical power at a rate of 60 watts while it is switched on.
12. Which formula is used to calculate electric power?
Answer: A. P = V × I
Electric power is calculated by multiplying the potential difference (voltage) across a conductor by the electric current flowing through it. This formula is widely used to determine the power consumed by electrical appliances and circuits.
Quick Revision:
- Formula: P = V × I
- P = Power
- V = Voltage
- I = Current
Real-Life Example:
The power rating printed on appliances such as fans, heaters, and electric irons is calculated using the relationship between voltage and current.
13. One kilowatt is equal to:
Answer: C. 1000 watts
The prefix “kilo” means one thousand. Therefore, one kilowatt (kW) is equal to 1000 watts (W). Large electrical appliances are usually rated in kilowatts because they consume more power.
Quick Revision:
- 1 kW = 1000 W
- “Kilo” means one thousand.
- High-power appliances are commonly rated in kW.
Real-Life Example:
An electric heater with a power rating of 2 kW consumes 2000 watts of electrical power.
14. Which of the following appliances generally consumes the highest electrical power?
Answer: D. Electric geyser
An electric geyser uses a high-power heating element to heat water quickly. Since heating requires a large amount of energy, a geyser consumes much more electrical power than appliances like LED bulbs, mobile chargers, or ceiling fans.
Quick Revision:
- Heating appliances consume more power.
- Electric geysers have high wattage.
- Higher power results in greater electricity consumption.
Real-Life Example:
Using an electric geyser for long periods can significantly increase your monthly electricity bill.
15. Which electrical device automatically disconnects the circuit during overload or short circuit?
Answer: C. MCB
A Miniature Circuit Breaker (MCB) is a protective device that automatically switches off the electrical supply when it detects an overload or short circuit. It protects electrical wiring and appliances from damage and can be reset after the fault is corrected.
Quick Revision:
- MCB trips automatically.
- Protects against overload and short circuits.
- Can be reset without replacement.
Real-Life Example:
If several high-power appliances are operated at the same time, the MCB may trip to protect the household electrical circuit.
16. Which of the following is the safest practice while handling electrical appliances?
Answer: D. Switch off the power before repairing electrical equipment
Switching off the power supply before repairing or servicing electrical equipment is the safest practice to prevent electric shock and accidental injuries. Working on live electrical circuits can be dangerous, so the power source should always be disconnected before carrying out any maintenance.
Quick Revision:
- Always switch off the power before repairs.
- Never handle electrical appliances with wet hands.
- Follow electrical safety rules to prevent accidents.
Real-Life Example:
An electrician always turns off the main power supply before repairing household wiring or replacing electrical switches.
17. The purpose of the neutral wire in domestic wiring is to:
Answer: B. Complete the electric circuit
The neutral wire provides the return path for electric current from the appliance back to the power source. It completes the electrical circuit, allowing current to flow continuously and enabling electrical appliances to operate properly.
Quick Revision:
- Neutral wire completes the circuit.
- Returns current to the power source.
- Works together with the live wire.
Real-Life Example:
A ceiling fan receives current through the live wire, and the current returns through the neutral wire to complete the circuit.
18. Which of the following is an advantage of connecting appliances in parallel?
Answer: A. If one appliance fails, the others continue to work
In a parallel circuit, each appliance is connected through a separate branch and receives the full supply voltage independently. Therefore, if one appliance stops working or is switched off, the remaining appliances continue to function normally.
Quick Revision:
- Appliances operate independently in parallel.
- Same voltage across each branch.
- Failure of one appliance does not affect the others.
Real-Life Example:
If one light bulb in your house burns out, the other lights continue to glow because they are connected in parallel.
19. Which electrical quantity is measured by an electricity meter in a house?
Answer: D. Electrical energy
A domestic electricity meter measures the total electrical energy consumed by all the electrical appliances in a house. The energy consumed is recorded in kilowatt-hours (kWh), which is the commercial unit used for calculating electricity bills.
Quick Revision:
- Electricity meter measures electrical energy.
- Unit used = Kilowatt-hour (kWh).
- Used to calculate electricity bills.
Real-Life Example:
The electricity board records the kWh reading from your home’s electricity meter every month to prepare your electricity bill.
20. Which of the following devices converts electrical energy mainly into heat energy?
Answer: A. Electric heater
An electric heater converts electrical energy into heat energy using a high-resistance heating element. It works on the heating effect of electric current, also known as Joule’s Law of Heating, making it suitable for heating rooms and water.
Quick Revision:
- Electric heater converts electrical energy into heat.
- Works on Joule’s heating effect.
- Uses a high-resistance heating element.
Real-Life Example:
Electric room heaters are commonly used during winter to keep homes warm by converting electricity into heat.
Further Reading:
To build a stronger foundation in electricity, explore the official NCERT Science textbook, which explains concepts such as electric potential, potential difference, electric current, Ohm’s law, resistance, resistivity, electrical circuits, and circuit symbols in a simple and systematic manner. Revisiting these topics will complement your TNPSC Physics Electricity Test 3 preparation, improve your understanding of TNPSC General Science Electricity, and help you solve Physics MCQs for TNPSC with greater confidence.
Further Reading: Chapter 11 – Electricity
