Electricity: Magnetic and Heating Effects — Quiz

Q1. Aakarsh places a magnetic compass below a straight wire and switches ON the circuit. He observes that the needle

• A. Continues to point along the wire as before
• B. Becomes very hot and snaps
• C. Gets deflected from its original direction
• D. Falls off from its pivot

Q2. Mohini deflects the compass needle by switching ON the circuit. When she moves the switch to OFF position, the needle

• A. Stays at the deflected position forever
• B. Returns to its original direction
• C. Spins very rapidly without stopping
• D. Points exactly opposite to its original direction

Q3. Ravi makes one electromagnet using a single cell and an identical one using a battery of three cells. The same coil and iron core are used. Which electromagnet picks up more iron clips?

• A. The single-cell electromagnet, because it gives more current
• B. Both will pick up the same number of clips
• C. The three-cell electromagnet, because it provides a larger current
• D. Neither will work as electromagnets need bigger cells

Q4. Priya wraps 30 turns of wire around an iron nail. Her friend wraps 80 turns around an identical nail. Both use the same cell. Whose electromagnet will be stronger?

• A. Priya's electromagnet with 30 turns
• B. Both will be equally strong since the cell is the same
• C. Priya's, because fewer turns give a thinner coil
• D. Her friend's electromagnet with 80 turns

Q5. Sumana's lifting electromagnet is holding many iron paper clips. As soon as she opens the switch, the clips

• A. Fall off, because the magnetic effect disappears with no current
• B. Stick more strongly to the nail
• C. Become permanently magnetised and stick to one another
• D. Begin to glow red hot

Q6. When electric current flows through a conductor, some of the electrical energy is converted into heat energy because

• A. The conductor is always wet
• B. The conductor offers resistance to the flow of current
• C. The current is always alternating current
• D. The conductor is a magnet

Q7. A nichrome wire and a copper wire of the same size and length carry the same current. Which one heats up more?

• A. The copper wire, because copper is a good conductor
• B. Both heat up equally because they carry the same current
• C. The nichrome wire, because it offers higher resistance than copper
• D. Neither heats up; metals never heat up with current

Q8. Which of the following pairs are both heating-effect appliances?

• A. Electric bell and electric fan
• B. Electric motor and loudspeaker
• C. Electric stove and electric iron
• D. Electric bell and electric kettle

Q9. Overheating in household appliances may cause damage to plugs and sockets where plastic parts melt or even lead to fires. To prevent this, one should

• A. Use wires, plugs and sockets rated for the specified electric current
• B. Use thinner wires to save money
• C. Remove the plastic covering of the wires
• D. Touch the wires with wet hands to check temperature

Q10. A Voltaic cell is set up as in the textbook figure. Which of the following is true about its two electrodes?

• A. Both rods are made of the same metal
• B. Both rods are made of plastic
• C. The two rods are made of different metals
• D. One rod is a magnet and the other a wooden stick

Q11. A Voltaic cell stops working after some time. According to the chapter, this happens because

• A. The wires become magnetic
• B. The chemicals inside the cell get used up
• C. The electrodes turn into insulators
• D. The container becomes hot

Q12. Neha makes a Voltaic cell using a lemon, with copper wire and an iron nail as electrodes. In her cell, the lemon juice acts as the

• A. Switch of the cell
• B. Heating element
• C. Wooden support
• D. Electrolyte

Q13. A crane operator at a scrap yard wants to drop the iron pieces lifted by his electromagnet. The simplest way to do this is to

• A. Pour water over the electromagnet
• B. Spray paint on the iron pieces
• C. Switch OFF the current to the electromagnet
• D. Replace the electromagnet with a torch

Q14. Which of these everyday devices typically uses a rechargeable battery as shown in Fig. 4.10 of the chapter?

• A. An ordinary wall clock
• B. A torch with two dry cells
• C. A mobile phone
• D. A wooden ruler

Q15. In the late 1700s, Luigi Galvani noticed that a dead frog's leg twitched when touched with two different metals — copper and iron. Galvani thought that

• A. The two metals were magnetic
• B. The frog's leg was burning
• C. The water in the room was hot
• D. The electricity came from the frog itself