Fill in the blanks:
a. Longer line in the symbol for a cell represents its ________terminal.
b. The combination of two or more cells is called a ______.
c. When current is switched ‘on’ in a room heater, it ___________.
d. The safety device based on the heating effect of electric current is called a _________.
Mark “T” if the statement is true and “F” if it is false:
a. To make a battery of two cells, the negative terminal of one cell is connected to the negative terminal of the other cell. (T/F)
b. When the electric current through the fuse exceeds a certain limit, the fuse wire melts and breaks. (T/F)
c. An electromagnet does not attract a piece of iron. (T/F)
d. An electric bell has an electro-magnet. (T/F)
Set up the circuit shown in Fig. 14.17 again. Move the key to ‘ON’ position and watch careful in which direction the compass needle gets deflected. Switch ‘OFF’ the current. Now keeping rest of the circuit intact, reverse the connections at the terminal of the cell. Again, switch ‘on’ the current. Note the direction in which the needle gets deflected. Think of an explanation.
Paheli and Boojho saw a magic trick sometime back. The magician placed an iron box on a stand. He then called Boojho and asked him to lift the box. Boojho could easily lift the box. Now the magician made a show of moving his stick around the box while muttering something. He again asked Boojho to lift the box. This time Boojho could not even move it. The magician again muttered something and not Boojho could lift the box.
The audience, including Paheli and Boojho, were very impressed with the show and felt that the magician had some supernatural powers. However, after reading this chapter Paheli wondering if the trick was indeed some magic or some science was involved? Can you guess what science might be involved?