Electric Current and Its Effects — Class 7 Science NCERT Solutions (Free)
Free step-by-step NCERT solutions for Class 7 Science chapter "Electric Current and Its Effects" — 8 important questions with detailed answers for CBSE board exam preparation.
TL;DR: Free step-by-step NCERT solutions for Class 7 Science chapter "Electric Current and Its Effects" — 8 important questions with detailed answers for CBS…
Written & reviewed by the Syllab.in Academic Team (CBSE/NCERT subject experts) · Updated
NCERT Solutions for Class 7 Science — Electric Current and Its Effects. Step-by-step answers to all 8 textbook questions from this chapter, written for CBSE board preparation and free to use.
Electric Current and Its Effects — All 8 Questions Solved
Q1. Define electric current. What is its SI unit?
Electric current: flow of electric charge through a conductor. It is the amount of charge flowing per unit time. Represented by symbol I. SI unit: Ampere (A), named after scientist André-Marie Ampère. 1 A = 1 Coulomb / 1 second (C/s).
Device: Ammeter measures current (connected in series in circuit).
Q2. What are the effects of electric current? Give examples.
Effects of electric current:
1. Heating effect: resistive heating in wires (electric heater, light bulb filament, fuse melts when current exceeds limit)
2. Magnetic effect: current carrying conductor creates magnetic field (electromagnet, electric bell, relay)
3. Chemical effect: chemical changes when current passes through solution (electroplating, electrolysis)
4. Lighting effect: current in gases produces light (neon tubes, discharge lamps)
Q3. Explain the magnetic effect of electric current.
When electric current flows through a conductor, it generates a magnetic field around the conductor. Direction of magnetic field follows right-hand rule: thumb points in direction of current, fingers curl in direction of field.
Applications: Electromagnet (solenoid with iron core produces strong magnet), Electric bell (electromagnet pulls armature), Relay (electromagnet controls switching), Motor (current in magnetic field produces force).
Q4. What is an electromagnet? How is it made?
Electromagnet: temporary magnet created by passing electric current through a coil of insulated wire wound around an iron core. How it works: current through coil creates magnetic field that magnetizes iron core.
Construction: Insulated copper wire wound in coil, iron rod inside coil, ends connected to power source.
Advantage: Strength can be controlled by varying current; magnetism disappears when current is switched off.
Q5. How does an electric bell work?
Working of electric bell:
Step 1: Current flows through electromagnet.
Step 2: Electromagnet attracts iron armature (attached to hammer).
Step 3: Hammer strikes the bell, producing sound.
Step 4: As armature moves, it breaks contact with screw, circuit opens.
Step 5: Electromagnet loses magnetism, spring pulls armature back.
Step 6: Contact is re-established, current flows again.
Step 7: Process repeats rapidly, producing continuous ringing.
Q6. What is the heating effect of electric current? Why does a fuse melt?
Heating effect: When electric current flows through a conductor, it generates heat due to resistance. Heat produced = I²Rt (Joule's law), where I = current, R = resistance, t = time.
Fuse: Thin wire of alloy (low melting point) in series with circuit. When current exceeds safe limit, excessive heat is produced, fuse wire melts, breaks circuit, prevents damage to appliances and fire hazard. Different appliances have different rated fuses.
Q7. Describe the circuit symbols for switch, bulb, battery, wire, and ammeter.
Circuit symbols (IEC standard):
- Battery/Cell: long line (positive) and short line (negative)
- Switch: break in line with small arm
- Resistor/Bulb: zigzag line or rectangle
- Wire: straight line
- Ammeter: circle with 'A' inside
- Ground: three horizontal lines
- Capacitor: two parallel lines
These symbols are used to draw circuit diagrams.
Q8. What is the difference between series and parallel circuits?
Series circuit: components connected one after another in single path. Current same through all; voltage divides. Total resistance increases. If one breaks, all stop. Used in strings of lights.
Parallel circuit: components connected in separate branches. Current divides among branches; voltage same across all. Total resistance decreases. If one breaks, others work. Used in home wiring.
Series: R_total = R1 + R2 + R3; Parallel: 1/R_total = 1/R1 + 1/R2 + 1/R3
Electric Current and Its Effects — Practice MCQs with Answers
Attempt these 20 multiple-choice questions after working through the solutions above. Each carries the correct option and the reasoning behind it, so a wrong answer tells you which idea to revisit.
MCQ 1. What is the primary function of an electric switch in a circuit?
- A. To convert electricity into heat
- B. To make or break the circuit
- C. To store electric current
- D. To increase the voltage
Answer: B. To make or break the circuit — An electric switch is used to complete or interrupt the flow of current in a circuit, thereby turning a device on or off.
MCQ 2. Which of the following devices works primarily on the heating effect of electric current?
- A. Electric fan
- B. Electric bell
- C. Electric heater
- D. Electromagnet
Answer: C. Electric heater — An electric heater uses a heating element that becomes hot when current passes through it, demonstrating the heating effect of electric current.
MCQ 3. The wire used in an electric fuse typically has a:
- A. High melting point and high resistance
- B. Low melting point and high resistance
- C. High melting point and low resistance
- D. Low melting point and low resistance
Answer: B. Low melting point and high resistance — A fuse wire is designed to melt quickly and break the circuit when an excessive current flows. This requires a low melting point and high resistance to heat up rapidly.
MCQ 4. Which textual description correctly represents the symbol for an electric cell in a circuit diagram?
- A. A longer line and a shorter, thicker parallel line
- B. A zig-zag line
- C. A circle with a cross inside
- D. Two parallel lines of equal length
Answer: A. A longer line and a shorter, thicker parallel line — The symbol for an electric cell consists of a longer line representing the positive terminal and a shorter, thicker parallel line representing the negative terminal.
MCQ 5. What happens to the filament of an incandescent light bulb when electric current passes through it?
- A. It cools down rapidly
- B. It becomes magnetically charged
- C. It heats up and glows brightly
- D. It expands and contracts repeatedly
Answer: C. It heats up and glows brightly — When electric current passes through the thin filament of an incandescent bulb, it heats up to a very high temperature, causing it to emit light and glow.
MCQ 6. Which effect of electric current is utilized in an electromagnet?
- A. Heating effect
- B. Chemical effect
- C. Magnetic effect
- D. Lighting effect
Answer: C. Magnetic effect — An electromagnet works on the principle that an electric current flowing through a coil of wire creates a magnetic field, which is the magnetic effect of electric current.
MCQ 7. An electric circuit is said to be an 'open circuit' when:
- A. Current flows continuously
- B. The switch is in the 'ON' position
- C. The path for current is broken
- D. It has a battery connected
Answer: C. The path for current is broken — An open circuit means there is a break in the path of the electric current, preventing it from flowing through the circuit.
MCQ 8. Why is an MCB (Miniature Circuit Breaker) often preferred over a traditional fuse in modern electrical installations?
- A. MCBs are cheaper to install than fuses
- B. MCBs need to be replaced every time they trip
- C. MCBs can be reset manually after tripping
- D. MCBs work on the chemical effect of current
Answer: C. MCBs can be reset manually after tripping — Unlike fuses which need to be replaced after blowing, an MCB automatically switches off in case of an overload or short circuit and can be easily reset by pushing a switch.
MCQ 9. A battery is essentially a combination of:
- A. Two resistors
- B. Two or more electric cells
- C. Two capacitors
- D. Two switches
Answer: B. Two or more electric cells — A battery is formed when two or more electric cells are connected together in series, providing a higher voltage.
MCQ 10. What observation led Hans Christian Oersted to discover the magnetic effect of electric current?
- A. A bulb glowing brighter near a current-carrying wire
- B. A compass needle deflecting near a current-carrying wire
- C. A wire getting hot when current passed through it
- D. Water boiling when current passed through it
Answer: B. A compass needle deflecting near a current-carrying wire — Oersted observed that a compass needle placed near a wire carrying electric current deflected, indicating the presence of a magnetic field around the current.
MCQ 11. Which of the following statements about an electromagnet is FALSE?
- A. Its strength can be increased by increasing the current
- B. It is a temporary magnet
- C. It can be easily demagnetized by switching off the current
- D. It attracts all types of materials
Answer: D. It attracts all types of materials — An electromagnet, like a permanent magnet, only attracts magnetic materials such as iron, cobalt, and nickel, not all types of materials.
MCQ 12. If the current in an electric circuit becomes excessively large, what is the most likely consequence for a properly installed fuse?
- A. The fuse wire will become stronger
- B. The fuse wire will melt and break the circuit
- C. The fuse wire will cool down
- D. The fuse will increase the voltage in the circuit
Answer: B. The fuse wire will melt and break the circuit — A fuse is a safety device designed to protect circuits from overcurrent. If the current exceeds its safe limit, the fuse wire melts due to excessive heating and breaks the circuit.
MCQ 13. Which of these is NOT typically considered a basic component of a simple electric circuit?
- A. Connecting wire
- B. Switch
- C. Table
- D. Electric cell
Answer: C. Table — A table is a piece of furniture and not an essential component required to form a basic electric circuit.
MCQ 14. Why do electricians advise using rubber gloves while working with electricity?
- A. Rubber gloves conduct electricity to ground
- B. Rubber gloves are good electrical insulators
- C. Rubber gloves are good conductors of heat
- D. Rubber gloves are primarily used for improved grip
Answer: B. Rubber gloves are good electrical insulators — Rubber is an insulator, meaning it does not allow electric current to pass through it easily. This protects electricians from electric shocks by preventing current flow through their bodies.
MCQ 15. In an electric bell, what is the primary role of the soft iron armature?
- A. To act as the gong that produces sound
- B. To connect directly to the battery as a power source
- C. To be attracted by the electromagnet and strike the gong
- D. To regulate the current flow in the circuit
Answer: C. To be attracted by the electromagnet and strike the gong — When the electromagnet is energized, it attracts the soft iron armature, causing the hammer attached to it to strike the gong and produce sound.
MCQ 16. The complete closed path along which electric current flows is called a/an:
- A. Electric road
- B. Electric current
- C. Electric circuit
- D. Electric pathway
Answer: C. Electric circuit — An electric circuit is the complete closed path through which electric current can flow from the source, through components, and back to the source.
MCQ 17. Which of the following best describes the energy transformation in an incandescent electric bulb?
- A. Electrical energy to mechanical energy
- B. Electrical energy to light energy only
- C. Electrical energy to heat and light energy
- D. Chemical energy to electrical energy
Answer: C. Electrical energy to heat and light energy — An incandescent bulb primarily converts electrical energy into heat, which then causes the filament to glow and produce light. A significant portion of energy is wasted as heat.
MCQ 18. What is the main characteristic of the wire material used in a heating element, such as in an electric iron or toaster?
- A. Low resistance
- B. High resistance
- C. Zero resistance
- D. Infinite resistance
Answer: B. High resistance — Heating elements are made of materials with high resistance, so they get very hot when electric current passes through them, producing the desired heating effect.
MCQ 19. An electric current passing through a wire produces a magnetic field around it. This effect is specifically used in which of the following applications?
- A. Electric toaster
- B. Electric geyser
- C. Electric crane
- D. Electric kettle
Answer: C. Electric crane — Electric cranes use powerful electromagnets to lift and transport heavy iron objects, utilizing the magnetic effect of electric current. Toasters, geysers, and kettles primarily use the heating effect.
MCQ 20. If you connect multiple cells to form a battery to increase the total voltage, what is the general rule for connecting them?
- A. Positive terminal to positive terminal
- B. Negative terminal to negative terminal
- C. Positive terminal of one cell to the negative terminal of the next
- D. All terminals of all cells connected together
Answer: C. Positive terminal of one cell to the negative terminal of the next — To form a battery and increase the total voltage, cells are connected in series, meaning the positive terminal of one cell is connected to the negative terminal of the next.
How to Use These Solutions
Attempt each question yourself first and only then compare with the worked answer. Marks in the CBSE board exam are awarded for the METHOD as much as the final result, so reproduce the steps rather than memorising the last line. Where a solution states a law, a formula or a definition, learn that wording — examiners look for it.
Related practice for this chapter: chapter MCQs, previous-year questions, revision notes and sample papers.