Boost your confidence with TNPSC Physics Electricity Test 5, featuring carefully selected Electricity MCQs based on the TNPSC Physics syllabus. Attempt this TNPSC Free Online Test to reinforce essential concepts, test your understanding, and move one step closer to success in the TNPSC exam.
TNPSC Physics Electricity Test 5 – Detailed Explanation For All Questions
A strong understanding of Electricity concepts is essential for answering TNPSC General Science questions accurately. The explanations in this test focus on important topics where Questions are asked such as electric circuits, resistance, conductors and insulators, electric power, electrical energy, household electricity, electrical safety, the heating effect of electric current, the magnetic effect of electric current, and their practical applications. Learning these concepts will help you answer similar TNPSC questions with greater confidence.
1. Which of the following is the SI unit of electrical conductivity?
Answer: Siemens per metre (S/m)
Electrical conductivity is the property of a material that indicates how easily electric current can pass through it. Materials with high electrical conductivity, such as copper and silver, allow electrons to move freely and are widely used in electrical wiring. The SI unit of electrical conductivity is siemens per metre (S/m). Conductivity is the reciprocal of resistivity, meaning materials with high conductivity have low electrical resistance.
Quick Revision:
- Electrical conductivity measures the ability of a material to conduct electricity.
- SI unit: Siemens per metre (S/m).
- High conductivity means low electrical resistance.
- Copper and silver are excellent conductors.
Real-Life Example:
Copper wires are used in household electrical wiring because their high electrical conductivity allows electricity to flow efficiently with minimal energy loss.
2. A conductor offers less resistance because it has:
Answer: More free electrons
Conductors contain a large number of free electrons that can move easily when a potential difference is applied. These freely moving electrons carry electric current through the material. Since the movement of electrons faces very little opposition, conductors have low electrical resistance. Metals such as copper, aluminium, and silver are good conductors because they have many free electrons.
Quick Revision:
- Conductors have many free electrons.
- Free electrons carry electric current.
- More free electrons result in lower resistance.
- Copper and aluminium are common conductors.
Real-Life Example:
Electrical cables use copper conductors because the large number of free electrons allows electricity to flow smoothly to electrical appliances.
3. Which of the following is not a good conductor of electricity?
Answer: Glass
Glass is an electrical insulator because it does not contain free electrons that can move easily. As a result, electric current cannot pass through it under normal conditions. Insulating materials are used to prevent electric shock and protect electrical equipment. Other common insulators include rubber, plastic, porcelain, and dry wood.
Quick Revision:
- Glass is an electrical insulator.
- Insulators have very few or no free electrons.
- Electric current does not flow easily through insulators.
- Rubber and plastic are also good insulators.
Real-Life Example:
Glass and porcelain are used in electric transmission line insulators to prevent electricity from leaking into supporting structures.
4. Which of the following quantities is measured using a voltmeter?
Answer: Potential difference
A voltmeter is an electrical instrument used to measure the potential difference (voltage) between two points in a circuit. It is always connected in parallel with the component whose voltage is being measured. A voltmeter has very high resistance so that it draws only a very small amount of current and does not affect the operation of the circuit.
Quick Revision:
- A voltmeter measures potential difference (voltage).
- Unit of voltage: Volt (V).
- Connected in parallel.
- Has very high internal resistance.
Real-Life Example:
Electricians use a voltmeter to check the voltage of batteries, household power supplies, and electrical circuits during maintenance.
5. The resistance of a wire decreases when its:
Answer: Cross-sectional area increases
The resistance of a conductor depends on its length, cross-sectional area, material, and temperature. A wire with a larger cross-sectional area provides more space for electrons to move, reducing opposition to current flow. Therefore, thicker wires have lower resistance than thinner wires made of the same material and length. This principle is widely applied in electrical wiring to minimize energy loss.
Quick Revision:
- Thicker wires have lower resistance.
- Resistance decreases as cross-sectional area increases.
- Longer wires have greater resistance.
- Copper wires are preferred because of their low resistivity.
Real-Life Example:
Heavy electrical appliances such as air conditioners and water heaters use thick copper wires to safely carry higher currents with less resistance.
6. Which of the following has the highest resistance?
Answer: Long, thin nichrome wire
The resistance of a conductor depends on its length, cross-sectional area, and the material from which it is made. A longer wire has greater resistance because electrons travel a longer distance. A thinner wire has less area for electron movement, increasing resistance. Nichrome also has a much higher resistivity than metals like copper or silver. Therefore, a long, thin nichrome wire offers the highest resistance among the given options.
Quick Revision:
- Resistance increases with length.
- Resistance decreases with cross-sectional area.
- Nichrome has high resistivity.
- Long, thin nichrome wires have high resistance.
Real-Life Example:
Nichrome wires are used as heating elements in electric irons, heaters, and toasters because their high resistance produces heat efficiently.
7. Electric current is produced in a circuit only when:
Answer: A complete conducting path exists
Electric current flows only when there is a closed circuit. A closed circuit provides a continuous conducting path from one terminal of the power source to the other. If the circuit is open due to a broken wire or an open switch, the flow of electrons stops, and no current passes through the circuit.
Quick Revision:
- Current flows only in a closed circuit.
- An open circuit stops the flow of electricity.
- A switch controls the opening and closing of a circuit.
- A continuous conducting path is essential for current flow.
Real-Life Example:
When you switch on a room light, the switch closes the circuit, allowing current to flow and the bulb to glow.
8. Which appliance mainly converts electrical energy into mechanical energy?
Answer: Electric fan
An electric fan contains an electric motor that converts electrical energy into mechanical energy. When electric current flows through the motor, it produces a magnetic field that rotates the motor shaft, causing the fan blades to spin. This mechanical motion circulates air in the room.
Quick Revision:
- Electric fans use electric motors.
- Electrical energy is converted into mechanical energy.
- Motors work based on the magnetic effect of electric current.
- Rotating blades produce airflow.
Real-Life Example:
Mixer grinders, water pumps, washing machines, and ceiling fans all use electric motors to convert electrical energy into mechanical motion.
9. Which safety device protects people from electric shock by providing a low-resistance path to the ground?
Answer: Earth wire
The earth wire is an important safety feature in household electrical wiring. It provides a low-resistance path for leakage current to flow safely into the ground. If the metal body of an electrical appliance becomes live due to insulation failure, the earth wire carries the excess current to the ground, reducing the risk of electric shock.
Quick Revision:
- Earth wire protects against electric shock.
- It provides a low-resistance path to the ground.
- Leakage current safely flows into the earth.
- Earthing improves electrical safety.
Real-Life Example:
The metal body of a refrigerator or washing machine is connected to an earth wire so that users remain safe even if an internal fault occurs.
10. Which of the following is an example of the magnetic effect of electric current?
Answer: Electric bell
When electric current passes through a coil of wire wound around a soft iron core, it produces a temporary magnet called an electromagnet. An electric bell uses this electromagnet to attract an iron armature, causing the hammer to strike the bell repeatedly. This demonstrates the magnetic effect of electric current.
Quick Revision:
- Electric current produces a magnetic field.
- A current-carrying coil acts as an electromagnet.
- Electric bells work using electromagnets.
- Electromagnets are temporary magnets.
Real-Life Example:
Electromagnets are also used in cranes to lift scrap iron, electric relays, loudspeakers, and doorbells.
11. Which property of a fuse wire makes it suitable for protection?
Answer: Low melting point
A fuse wire is a safety device used to protect electrical circuits from excessive current. It is made of a material with a low melting point. When the current flowing through the circuit exceeds the safe limit, the fuse wire becomes hot due to the heating effect of electric current and melts. This breaks the circuit immediately, preventing damage to electrical appliances and reducing the risk of fire.
Quick Revision:
- A fuse protects electrical circuits from overcurrent.
- Fuse wire has a low melting point.
- Excess current melts the fuse wire.
- The circuit is automatically disconnected.
Real-Life Example:
Household electrical installations use fuse wires or MCBs to protect wiring and appliances from damage caused by short circuits or overloads.
12. Which wire is usually connected through the fuse in household wiring?
Answer: Live wire
In household wiring, the fuse is always connected in the live wire. During a fault or excessive current flow, the fuse melts and disconnects the live supply from the appliance. If the fuse were connected in the neutral wire, the appliance could still remain connected to the live supply, increasing the risk of electric shock. Therefore, placing the fuse in the live wire ensures better electrical safety.
Quick Revision:
- The fuse is connected in the live wire.
- It disconnects the live supply during a fault.
- This helps prevent electric shock.
- Neutral and earth wires are not connected through the fuse.
Real-Life Example:
The fuse inside a household plug is connected to the live wire to protect both the appliance and the user from electrical hazards.
13. Which factor remains the same for all appliances connected in parallel?
Answer: Voltage
In a parallel circuit, all appliances are connected across the same two supply points. Therefore, each appliance receives the full supply voltage regardless of its resistance or power rating. This is why household electrical wiring is connected in parallel, allowing each appliance to operate independently without affecting the others.
Quick Revision:
- Voltage is the same across all parallel branches.
- Current divides according to the resistance of each branch.
- Household wiring uses parallel connections.
- Appliances work independently in a parallel circuit.
Real-Life Example:
In a house, switching off a fan does not affect the operation of lights or other appliances because they are connected in parallel.
14. One unit of electrical energy is equal to:
Answer: 1 kWh
Electrical energy is the amount of work done or power consumed over a period of time. The commercial unit used by electricity boards is the kilowatt-hour (kWh). One kilowatt-hour means using an electrical appliance with a power rating of 1 kilowatt for one hour. This unit is commonly called one unit of electricity and is used to calculate electricity bills.
Quick Revision:
- One commercial unit = 1 kWh.
- 1 kWh = 1000 watt-hours.
- Electricity consumption is measured in kWh.
- Electricity bills are based on the number of units consumed.
Real-Life Example:
If a 1000 W electric heater operates for one hour, it consumes one unit (1 kWh) of electrical energy.
15. Which device converts chemical energy directly into electrical energy?
Answer: Cell
An electric cell converts the chemical energy stored inside it directly into electrical energy through chemical reactions. When the terminals of the cell are connected in a circuit, these reactions produce a flow of electrons, creating electric current. Dry cells, rechargeable batteries, and storage batteries all operate on this principle.
Quick Revision:
- A cell converts chemical energy into electrical energy.
- Chemical reactions produce electric current.
- Batteries consist of one or more electric cells.
- Cells are portable sources of electricity.
Real-Life Example:
Remote controls, wall clocks, flashlights, and toys use dry cells or batteries to supply electrical energy without requiring a direct power connection.
16. Which of the following is the safest action before replacing a fused bulb?
Answer: Switch OFF the main power supply
Electrical safety should always be the first priority when handling electrical appliances or repairing electrical circuits. Before replacing a fused bulb, the main power supply should be switched OFF to ensure that no electric current is flowing through the circuit. This eliminates the risk of accidental electric shock while touching the bulb holder or wiring. Simply wearing rubber slippers is not a substitute for disconnecting the power supply.
Quick Revision:
- Always switch OFF the main power supply before electrical repairs.
- Never touch live electrical components.
- Disconnecting the supply prevents electric shock.
- Follow basic electrical safety rules at home and in workplaces.
Real-Life Example:
Before changing a ceiling bulb or repairing a switchboard, electricians first turn OFF the main switch to ensure safe working conditions.
17. The flow of electrons in a metallic conductor is from:
Answer: Negative terminal to positive terminal
In metallic conductors, electric current is carried by free electrons. These electrons move from the negative terminal of the power source towards the positive terminal when the circuit is complete. However, by convention, the direction of electric current is considered to be from the positive terminal to the negative terminal. Understanding the difference between electron flow and conventional current is important for competitive examinations like TNPSC.
Quick Revision:
- Electrons flow from negative to positive terminal.
- Conventional current flows from positive to negative terminal.
- Metals conduct electricity through free electrons.
- Electron flow and conventional current are opposite in direction.
Real-Life Example:
In a battery-powered torch, electrons travel from the negative terminal through the circuit to the positive terminal, causing the bulb to glow.
18. Which of the following materials is commonly used to cover electric wires?
Answer: Plastic
Plastic is widely used to cover electrical wires because it is an excellent electrical insulator. It prevents electric current from escaping the conductor and protects people from accidental electric shock. In addition to being a poor conductor of electricity, plastic is durable, flexible, lightweight, and resistant to moisture, making it suitable for insulating household and industrial electrical cables.
Quick Revision:
- Plastic is an electrical insulator.
- It prevents electric shock.
- It protects the conducting wire from damage.
- Rubber and PVC are also commonly used as insulating materials.
Real-Life Example:
The coloured coating around household electrical wires is usually made of PVC plastic, which safely insulates the copper conductor inside.
19. Which appliance generally consumes the least electrical energy during one hour of use?
Answer: LED bulb
The amount of electrical energy consumed by an appliance depends on its power rating and the duration of use. LED bulbs have very low power consumption compared to appliances such as room heaters, electric irons, and geysers. They produce bright light while using much less electricity, making them one of the most energy-efficient lighting options available today.
Quick Revision:
- Electrical energy consumption depends on power and time.
- LED bulbs have very low power consumption.
- Heating appliances consume much more electricity.
- Energy-efficient appliances reduce electricity bills.
Real-Life Example:
Replacing traditional incandescent bulbs with LED bulbs in a home significantly reduces monthly electricity consumption and lowers energy costs.
20. Which statement about electricity is correct?
Answer: Good conductors have low electrical resistance.
Good conductors, such as copper, silver, and aluminium, have low electrical resistance, allowing electric current to flow easily through them. In contrast, insulators like rubber, glass, and plastic have very high resistance and restrict the flow of current. This difference in electrical resistance determines whether a material is suitable for conducting electricity or for providing insulation and safety.
Quick Revision:
- Good conductors have low electrical resistance.
- Copper and silver are excellent conductors.
- Insulators have very high resistance.
- Electrical resistance opposes the flow of current.
Real-Life Example:
Copper is used for electrical wiring because its low resistance allows electricity to be transmitted efficiently with minimal energy loss.
Quick Revision :
- Electric current flows only in a closed circuit with a complete conducting path.
- The SI unit of electrical conductivity is siemens per metre (S/m), while resistance is measured in ohms (Ω).
- Good conductors have low electrical resistance because they contain many free electrons.
- The resistance of a wire increases with its length and decreases with its cross-sectional area.
- A voltmeter measures potential difference and is always connected in parallel.
- Household electrical wiring uses parallel circuits so that each appliance receives the full supply voltage.
- Fuse wires have a low melting point and protect electrical circuits from excessive current.
- The fuse is connected in the live wire to disconnect the power supply during a fault.
- Earthing provides a low-resistance path for leakage current and helps prevent electric shock.
- One commercial unit of electrical energy is equal to one kilowatt-hour (1 kWh).
- Electric motors convert electrical energy into mechanical energy, while electric cells convert chemical energy into electrical energy.
- Always switch OFF the main power supply before carrying out any electrical repair or maintenance.
Further Reading:
Continue your preparation by studying the Electricity chapters in the NCERT Science textbooks and Tamil Nadu State Board Science books. Revising these concepts alongside the explanations in this test will improve your conceptual understanding and help you answer TNPSC General Science questions with greater accuracy.
NCERT Link: Chapter 11 – Electricity
