Electricity: Magnetic and Heating Effects
Class 8 · Science · 11 Questions
Fill in the blanks: (i) The solution used in a Voltaic cell is called ____. (ii) A current carrying coil behaves like a ____.
Choose the correct option: (i) Dry cells are less portable compared to Voltaic cells. (True/False) (ii) A coil becomes an electromagnet only when electric current flows through it. (True/False) (iii) An electromagnet, using a single cell, attracts more iron paper clips than the same electromagnet with a battery of 2 cells. (True/False)
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. Choose the correct option
Match the items in Column A with those in Column B.
| Column A | Column B |
|---|---|
| (i) Voltaic cell | (a) Best suited for electric heater |
| (ii) Electric iron | (b) Works on magnetic effect of electric current |
| (iii) Nichrome wire | (c) Works on heating effect of electric current |
| (iv) Electromagnet | (d) Generates electricity by chemical reactions |
Nichrome wire is commonly used in electrical heating devices because it (i) is a good conductor of electricity. (ii) generates more heat for a given current. (iii) is cheaper than copper. (iv) is an insulator of electricity.
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 reason(s) to support this statement considering societal impact.
Suppose Sumana forgets to move the switch of her lifting electromagnet model to OFF position (in introduction story). 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.
Neha keeps the coil exactly the same as in Activity 4.4 but slides the iron nail out, leaving only the coiled wire. Will the coil still deflect the compass? If yes, will the deflection be more or less than before?
Make coils of turns 25, 50, 75, and 100. Connect them to the same cell one by one. Note the deflection in a magnetic compass placed in the same position in all the cases. Report your observations. Draw conclusion of the effect of number of turns of the coil on the strength of the electromagnet.
Take two thin nichrome wires of equal length and different thickness (approximately one of these wire thickness to be double of the other, say 0.3 mm and 0.6 mm). Connect them one by one in a circuit which has a switch and a cell, and allow the current to flow for 30 s in each case. Momentarily touch these wires. Which wire heats up more? Now repeat the same activity with two nichrome wires of same diameter but of different lengths. Prepare a brief report of your activity.
Try to make an electric cell using various fruits and vegetables. Also try with electrodes of different metals. Prepare a brief report.