ELECTRICITY, CIRCUITS AND THEIR COMPONENTS Class 7 : Science : Question and Answers
SUMMARY:
What is Electricity?
Electricity is a form of energy produced due to the movement of electrons (tiny particles with negative charge).
It flows in a path called an electric circuit.
Electric Circuit
A closed path through which electric current flows.
If the circuit is broken/open → current does not flow.
Essential components of a circuit:
Cell/Battery – provides energy (source).
Switch – controls flow (ON/OFF).
Bulb/Appliance – device that uses the current.
Wires – provide conducting path.
Symbols in a Circuit Diagram
Standard symbols are used to represent components:
Cell: | |
Battery: series of cells
Bulb: ⚫ with cross inside
Switch: (open or closed)
Wire: straight line
Conductors and Insulators
Conductors: materials that allow current to flow (copper, aluminium, water with salts).
Insulators: materials that do not allow current to flow (plastic, rubber, wood).
Electric Current
The flow of charges (electrons) in a circuit.
Measured in amperes (A) using an ammeter.
Heating Effect of Electric Current
When current passes through a wire or filament, it produces heat.
Applications:
Electric bulb (filament glows).
Electric iron, heater, toaster.
Magnetic Effect of Electric Current
Current in a wire produces a magnetic field around it.
Basis of electromagnets and electric bells.
Electric Safety
Excess current can cause short circuits and fires.
Fuse: A safety device that melts and breaks the circuit if current is too high.
Modern houses use MCBs (Miniature Circuit Breakers).
Key Points to Remember
A complete circuit is required for current to flow.
Cell/battery is the source of electrical energy.
Switch controls electricity flow.
Conductors and insulators play different roles in circuit building.
Electricity can produce heat, light, and magnetism.
Safety devices like fuses protect us from accidents.
SHORT QUESTION–ANSWERS
Q: What is electricity?
A: Electricity is a form of energy caused by the flow of electrons through a conductor.
Q: What is an electric circuit?
A: An electric circuit is a closed path through which current flows.
Q: Name the main components of an electric circuit.
A: Cell/battery, switch, bulb/appliance, connecting wires.
Q: What is the symbol of a cell in circuit diagrams?
A: A short and a long parallel line.
Q: What is the symbol of a battery?
A: Several cells connected in series.
Q: What happens if a circuit is open?
A: Current does not flow.
Q: What is a conductor?
A: A material that allows electricity to pass through (e.g., copper).
Q: What is an insulator?
A: A material that does not allow current to pass through (e.g., rubber).
Q: Name two good conductors.
A: Copper and aluminium.
Q: Name two insulators.
A: Plastic and wood.
Q: What is the function of a switch?
A: It controls the flow of current in a circuit.
Q: What is the unit of electric current?
A: Ampere (A).
Q: What instrument is used to measure current?
A: Ammeter.
Q: What is the heating effect of current?
A: Current produces heat when it flows through a conductor.
Q: Give one use of heating effect of current.
A: Used in electric irons.
Q: What is the magnetic effect of current?
A: Current produces a magnetic field around the conductor.
Q: Name one device that works on magnetic effect of current.
A: Electric bell.
Q: What is a fuse?
A: A safety device that melts when excess current flows.
Q: Why is fuse wire made of tin-lead alloy?
A: Because it has low melting point.
Q: What is MCB?
A: Miniature Circuit Breaker, a modern safety device.
Q: What is the source of energy in an electric circuit?
A: Cell or battery.
Q: Why does a bulb glow?
A: Because current heats its filament and produces light.
Q: Name the filament material of an electric bulb.
A: Tungsten.
Q: What is short circuit?
A: Direct connection of positive and negative terminals without resistance.
Q: What can happen due to short circuit?
A: Fire accidents.
Q: What is an electric cell?
A: A device that converts chemical energy into electrical energy.
Q: What is the symbol of a bulb?
A: A circle with a cross inside.
Q: Why are wires coated with plastic?
A: To prevent electric shocks.
Q: What are connecting wires made of?
A: Copper or aluminium.
Q: Why are metals good conductors?
A: Because they contain free electrons.
Q: What is an electromagnet?
A: A magnet formed when current flows through a coil of wire around iron.
Q: Where are electromagnets used?
A: In cranes, electric bells, motors.
Q: What is the difference between open and closed circuit?
A: Open circuit → no current flow; Closed circuit → current flows.
Q: What safety rule should be followed with electricity?
A: Do not touch electric appliances with wet hands.
Q: What is the role of an electric switchboard?
A: To distribute and control electricity safely in a house.
LONG QUESTION–ANSWERS
Q: Define an electric circuit. Explain with a neat diagram the essential components of a simple circuit.
A: An electric circuit is a closed path through which current flows. Essential parts are:
Cell/Battery – source of energy
Wires – conducting path
Switch – controls flow
Bulb/Appliance – device using current.
When connected properly in a closed loop, current flows and the bulb glows.
Q: Differentiate between an open and closed circuit with diagrams.
A:Open Circuit – Switch is OFF, no current flows, bulb does not glow.
Closed Circuit – Switch is ON, current flows, bulb glows.
Q: What is a conductor? Give examples and explain why metals are good conductors.
A: A conductor allows current to flow. Examples: copper, aluminium. Metals are good conductors because they have free-moving electrons.
Q: What is an insulator? Give examples and state its importance.
A: An insulator resists current flow. Examples: plastic, rubber, wood. Importance: prevents electric shock, used for wire covering.
Q: Explain the heating effect of electric current with applications.
A: When current flows, it produces heat. Applications: electric iron, heater, toaster, bulb filament.
Q: What is the magnetic effect of current? Demonstrate with an activity.
A: Current produces magnetism around a wire. Activity: Place a compass near a wire carrying current, needle deflects. Used in electromagnets.
Q: Write the differences between conductors and insulators.
A:Conductors: allow current, e.g., copper.
Insulators: block current, e.g., plastic.
Conductors used in wires, insulators used as covering.
Q: Explain the function and symbol of a switch in an electric circuit.
A: A switch opens/closes a circuit. Symbol: “gap in line” (open), “joined line” (closed).
Q: What is the importance of electric symbols? Give four examples.
A: Symbols make diagrams simple and universal. Examples: Cell, Battery, Bulb, Switch.
Q: What is an electric cell? Explain how it works.
A: A cell converts chemical energy into electrical energy. It has positive and negative terminals. When connected in a circuit, electrons flow producing current.
Q: Explain the function of a fuse in detail.
A: Fuse is a thin wire that melts and breaks the circuit if current is high. It prevents fire accidents and damage to appliances.
Q: What are MCBs? Why are they preferred over fuses?
A: MCB = Miniature Circuit Breaker. It trips automatically when excess current flows. Unlike fuses, they can be reused and are safer.
Q: What is a short circuit? How can it be prevented?
A: Short circuit is direct connection of positive and negative wires with little resistance. Causes fire. Prevention: use proper insulation, fuse, MCBs.
Q: Why should wires be covered with plastic?
A: To insulate conductors, prevent shocks and fire. Plastic is a good insulator.
Q: What is an electromagnet? Explain its construction and uses.
A: Coil of insulated wire wound on soft iron core carrying current. Strong magnet when current flows. Uses: cranes, electric bells, motors.
Q: Explain why tungsten is used in electric bulb filaments.
A: Tungsten has high melting point (3380°C) and glows when heated. Durable and efficient for bulbs.
Q: Explain with examples how electricity is useful in our daily life.
A: Electricity gives light (bulbs, lamps), heat (iron, heater), sound (radio), motion (fans, motors).
Q: Describe safety measures while using electricity.
A: Do not touch appliances with wet hands, use fuse/MCB, proper insulation, avoid overload, earthing of wires.
Q: What is the function of an ammeter? How is it connected in a circuit?
A: Ammeter measures current in amperes. Connected in series with the circuit.
Q: Compare series and parallel connection of batteries.
A: Series: voltages add up, gives more energy. Parallel: increases current capacity, long-lasting.
Q: What happens when excess current flows through wires?
A: Wires heat up, may cause fire, damage to appliances. Fuse/MCB stops it.
Q: Explain how electric bell works.
A: Bell has electromagnet, hammer and gong. When current flows, electromagnet attracts hammer, which strikes gong producing sound.
Q: What is a battery? How is it different from a cell?
A: Battery = group of cells connected together. Provides more power than a single cell.
Q: Why should we not overload plug points?
A: Overload → heating of wires → risk of fire.
Q: Explain why salt water is a good conductor.
A: Salt water contains ions which allow current to pass.
Q: What happens when a fuse wire melts?
A: The circuit breaks, current stops, preventing damage.
Q: Write short notes on the uses of electricity in industries.
A: Runs machines, motors, furnaces, lighting, welding, chemical processing.
Q: What are connecting wires? Why is copper used?
A: Wires carry current. Copper is used because it has low resistance and high conductivity.
Q: What is the difference between AC and DC?
A: AC = Alternating Current (changes direction). DC = Direct Current (flows in one direction).
Q: Explain earthing and its importance.
A: Earthing provides a safe path for leakage current to flow to the ground. Prevents electric shocks.
Q: Describe how an electric bulb produces light.
A: Current passes through tungsten filament, it heats up and glows, producing light.
Q: State differences between fuse and MCB.
A: Fuse melts and must be replaced; MCB trips and can be reset.
Q: Why should we never touch live wires with bare hands?
A: Current can cause severe shock, burns or death.
Q: Explain applications of electromagnets.
A: Used in electric bells, telephones, cranes to lift heavy metals, motors, generators.
Q: Why is electricity called a versatile source of energy?
A: Because it can be converted into light, heat, motion, sound, magnetism.
MULTIPLE CHOICE QUESTIONS
1. Electricity is the flow of –
a) Protons
b) Electrons ✅
c) Neutrons
d) Atoms
2. The path of electric current is called –
a) Conductor
b) Circuit ✅
c) Insulator
d) Magnet
3. Which of these is a good conductor?
a) Rubber
b) Wood
c) Copper ✅
d) Plastic
4. Which is an insulator?
a) Aluminium
b) Iron
c) Plastic ✅
d) Silver
5. A bulb glows only in –
a) Open circuit
b) Closed circuit ✅
c) Short circuit
d) Broken circuit
6. Symbol of battery is –
a) Single line
b) Two cells in series ✅
c) Circle with cross
d) Switch
7. The unit of current is –
a) Volt
b) Ohm
c) Ampere ✅
d) Watt
8. Instrument to measure current –
a) Voltmeter
b) Ammeter ✅
c) Galvanometer
d) Ohmmeter
9. Filament of bulb is made of –
a) Copper
b) Aluminium
c) Tungsten ✅
d) Silver
10. Which effect makes bulb filament glow?
a) Magnetic
b) Heating ✅
c) Chemical
d) None
11. Electromagnet is based on –
a) Heating effect
b) Magnetic effect ✅
c) Chemical effect
d) None
12. Device used for safety –
a) Switch
b) Fuse ✅
c) Bulb
d) Ammeter
13. Fuse wire is made of –
a) Copper
b) Aluminium
c) Tin-lead alloy ✅
d) Silver
14. MCB stands for –
a) Miniature Current Breaker
b) Miniature Circuit Breaker ✅
c) Maximum Current Box
d) Main Circuit Board
15. Current flows from –
a) Positive to negative ✅ (conventional)
b) Negative to positive (electrons)
c) Both
d) None
16. Overload causes –
a) Cooling
b) Fire ✅
c) Light
d) Magnetism
17. Wire coating is made of –
a) Metal
b) Plastic ✅
c) Glass
d) Silver
18. Battery is –
a) Single cell
b) Group of cells ✅
c) Switch
d) None
19. Salt solution is –
a) Conductor ✅
b) Insulator
c) Magnet
d) Plastic
20. Short circuit occurs due to –
a) Proper connection
b) Direct contact of wires ✅
c) Use of fuse
d) Switch off
21. Electric bell works on –
a) Heating effect
b) Magnetic effect ✅
c) Chemical effect
d) Light effect
22. Example of appliance using heating effect –
a) Motor
b) Iron ✅
c) Fan
d) Radio
23. Which is safer?
a) Fuse
b) MCB ✅
c) Open wire
d) Bare wire
24. Ammeter is connected –
a) Parallel
b) Series ✅
c) Both
d) None
25. A bulb not glowing means –
a) Open circuit ✅
b) Closed circuit
c) Overload
d) Short circuit
26. Electricity can produce –
a) Heat
b) Light
c) Magnetism
d) All ✅
27. Tungsten has –
a) Low melting point
b) High melting point ✅
c) Medium
d) No melting point
28. Which prevents shock?
a) Fuse
b) Plastic coating ✅
c) Switch
d) Iron rod
29. A live wire is –
a) Safe to touch
b) Dangerous ✅
c) Insulated
d) Plastic
30. Electrons flow from –
a) Positive to negative
b) Negative to positive ✅
c) Both
d) None
31. Symbol of bulb is –
a) Circle with cross ✅
b) Circle with line
c) Two parallel lines
d) Open gap
32. Earthing provides –
a) Light
b) Safe path for leakage current ✅
c) Heat
d) Magnet
33. Example of device with electromagnet –
a) Bulb
b) Bell ✅
c) Switch
d) Battery
34. Electricity is called versatile because –
a) Easy to produce
b) Can be converted into many forms ✅
c) Cheap
d) Safe
35. The part of bulb that glows is –
a) Glass
b) Filament ✅
c) Base
d) Wire
