Class 8 Science Electricity Question Paper (25 Marks) – Heating and Magnetic Effect | USP Indore

Topics Covered in This Question Paper

• Electric circu—detectingng current flow without a lamp (alternate methods)
• Temporary magnets — how to make them
• Heating effect of electric current — how heat is generated in electrical appliances
• Dead cells and batteri—howow tidentify whichch can be recharged
• Voltaic cell — electrolyte solution
A current-carryingng coil and its magnetic behaviour
• Dry cells vs Voltaic cel—comparisonon (portability)
• Electromagnet — conditions for working; effect of number of cells on strength
• Nichrome wire — heating and magnetic effects simultaneously
• Matching: Voltaic cell, electric iron, nichrome wire, electromagnet
• Why nichrome wire is used in electrical heating devices
• Electric heating devices vs traditional metho—societalal impact
• Electromagnet model — why it stops working (Sumana\'s story from NCERT)
• LED circu—lemonon juice vs pure water as conductors
• Four coils (iron, copperaluminum, andm, nichrome) — compass needle deflection

All 16 Questions at a Glance

Q1 [3M]. If we don\'t have an electric lamp while making an electric circuit with an electric cell, is there any other way to find out if current is flowing in the circuit?

Q2 [2M]. Is it possible to make temporary magnets? How can these be made?

Q3 [2M]. We can generate heat by burning fossil fuels and wood, but how is heat generated in various electrical appliances?

Q4 [3M]. How do we know if a cell or a battery is dead? Can all cells and batteries be recharged?

Q5 [1M] Fill in the blank. The solution used in a voltaic cell is called ________.

Q6 [1M] Fill in the blank. A current carrying coil behaves like a ________.

Q7 [1M]: True or False. Dry cells are less portable compared to voltaic cells.

Q8 [1M]: True or False. A coil becomes an electromagnet only when electric current flows through it.

Q9 [1M] True or False. An electromagnet, using a single cell, attracts more iron paper clips than the same electromagnet with a battery of 2 cells.

Q10 [1M] MCQ. An electric current flows through a nichrome wire for a short time. (i) The wire becomes warm. (ii) A magnetic compass placed below the wire is deflected. Which option is correct?
(a) Both (i) and (ii) are not correct   (b) Only (i) (i) is correct   (c) Both (i) and (ii) are correct   (d) Only (ii) is correct

Q11 [2M] Match the columns.
Column A: (i) Voltaic cell | (ii) Electric iron | (iii) Nichrome wire | (iv) Electromagnet
Column B: (a) Best suited for electric heater | (b) Works on magnetic effect of electric current | (c) Works on heating effect of electric current | (d) Generates electricity by chemical reactions

Q12 [1M] MCQ. Nichrome wire is commonly used in electrical heating devices because it:
(a) is an insulator of electricity   (b) is a good conductor of electricity   (c) generates more heat for a given current   (d) is cheaper than copper

Q13 [2M]. Electric heating devices (like an electric heater or a stove) are often considered more convenient than traditional heating methods (like burning firewood or charcoal). Give reasons to support this statement considering societal impact.

Q14 [1M]. Suppose Sumana forgets to move the switch of her lifting electromagnet model to the OFF position. After some time, the iron nail no longer picks up the iron paper clips, but the wire wrapped around the iron nail is still warm. Why did the lifting electromagnet stop lifting the clips? Give possible reasons.

Q15 [2M] MCQ with Figure: In which case will the LED glow when the switch is closed? Circuit (a): iron nail and copper strip in lemon juice. Circuit (b): iron nail and copper strip in pure water.
(a) In all four circuits   (b) Only in circuits (a) and (b)   (c) Only in circuits (a), (b), and (c)   (d) Only in circuit (a)

Q16 [1M] MCQ with a figure. Four coils of similar shape and size are made from iron, copper, aluminum, and nichrome. When current is passed through all four coils, compass needles placed near them will show deflection. Which option correctly describes this?
(a) In all four circuits   (b) Only in circuits (a) and (b)   (c) Only in circuits (a), (b), and (c)   (d) Only in circuit (a)

Key Concepts Tested in This Paper

• Detecting current without a lamp: A magnetic compass placed near a wire deflects when current flo—thisis is the magnetic effect of electric current and can be used as an alternate detector.
• Temporary magnet: An iron nail can be made into a temporary magnet by winding insulated copper wire around it anconnecting itng to a batte—thisis is an electromagnet. It works only when current flows.
• Heating effect of electricity: When current flows through a conductor, it faces resistance, and the electrical energy converts into heat energy. This is the basis of all electric heating appliances.
• Dead cell/battery: A cell is dead when its chemical energy is fully used up and it can no longer produce electricity. Only secondary cells (like lead-acid batteries) can be recharged; primary cells (dry cells, Voltaic cells) cannot.
• Voltaic cell electrolyte: The solution used in a voltaic cell is dilute sulfuric acid (H₂SO₄)—called the electrolyte.
• Current-carrying coil: A coil carrying electric current behaves like a magnet (bar magne—itit has a north pole and south pole and creates a magnetic field around it.
• Dry celvs.vs Voltaic cell: Dry cells are MORE portable than Voltaic cells (which use liquid electrolyte and can spill). So the statement \"Dry cells are less portable\" is FALSE.
• Electromagnet strength: More cells in a battery → more current → stronger electromagnet → more paper clips attracted. A single-cell electromagnet attracts FEWER clips than a 2-cell electromagnet. So the given statement is FALSE.
• Nichrome wire: Used in heating devices because it has HIGH resistance and generates more heat for a given current. It also has a high melting point and does not oxidize easily.
• Lemon juicvs.vs pure water: Lemon juice is an electrolyte (conducts electricit—LED glows. s. Pure water is a very poor conductor—LED does NOT glow.
• All four coils (iron, copperaluminum, andm, nichrome): All four conducelectricity,ty and all four produce a magnetic field when current flo—compassss needles deflect in ALL four cases.

Important FAQs — Class 8 Science Electricity

Q. What is the heating effect of electric current?
Ans. When electric current flows through a conductor, the conductor resists the flow of electrons. This resistance causes electrical energy to be converted into heat energy. This is called the heating effect of electric current. It is used in electric irons, geysers, toasters, electric heaters, and incandescent bulbs.

Q. What is an electromagnet? How is it made?
Ans. An electromagnet is a temporary magnet made by winding insulated copper wire (coil) around an iron core (like an iron nail) and passing electric current through it. When current flows, the coil creates a magnetic field and the iron core becomes magnetized. When the current is switched off, the iron nail loses its magnetism—hence, it is a TEMPORARY magnet.

Q. Why is nichrome wire used in electric heating devices?
Ans. Nichrome wire is used in electric heaters and irons because (1) It has very HIGH resistance, so it generates more heat for a given current; (2) It has a very high melting point, so it does not melt even when very hot; (3) It does not oxidize (corrode) easily even at high temperatures. This makes it ideal for heating elements.

Q. What is the difference between primary and secondary cells?
Ans. Primary cells (like dry cells and Voltaic cells) cannot be recharged once they run out—the chemical reaction inside is irreversible. Secondary cells (like lead-acid batteries used in vehicles and rechargeable lithium-ion batteries in phones) can be recharged by passing electric current through them in the reverse direction.

Q. Why does lemon juice conduct electricity but pure water does not?
Ans. Lemon juice contains citric acid, which dissociates into ions (charged particles) when dissolved. These ions are free to move and carry electric charge—making lemon juice a conductor (electrolyte). Pure water has very few free ions and is therefore a very poor conductor of electricity. That is why an LED glows in lemon juice but not in pure water.

Q. How does increasing the number of cells affect an electromagnet?
Ans. Increasing the number of cells in a battery increases the voltage, which increases the current flowing through the coil. More current means a stronger magnetic field, which means the electromagnet can attract more iron objects. So a 2-cell battery makes a stronger electromagnet than a single cell.

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