Short Answers - Chemical Effects of Electric Current, Science, Class 8 PDF Download

SHORT ANSWER TYPE QUESTIONS
 

Q. 1. What do you mean by electric current?
Ans. The continuous and directional flow of charges (electrons) is called electric current. It is denoted by I and its unit is ampere.

Q. 2. What is a tester?
Ans. The instrument which is used to check the flow of electric current is called tester. It is attached to the terminals of the electric circuit. If the bulb of tester glows, it confirms that current is flowing through the circuit.
 

Q. 3. How can you test whether the liquids conduct or do not conduct the electricity?
Ans. Some liquids are the good conductors of electricity while some are poor conductors. The liquids can be tested for conductor of electricity. The free ends of a tester are dipped in liquid to be tested and then observe the bulb, if it glows, it confirms that the liquid is good conductor otherwise liquid is a poor conductor.
 

Q. 4. Show that lemon juice and vinegar are good conductors of electricity.
Ans. Collect a few plastic or rubber caps of bottles. Pour one teaspoon of lemon juice or vinegar in one cap. Bring the tester over the cap and let the ends of the tester dip into lemon juice or vinegar. We see that bulb starts to glow. It indicates that lemon juice and vinegar are good conductors of electricity.

Q. 5. Explain the mechanism of glowing of bulb in liquid.
Ans. When the liquid between the two ends of a tester allows the electric current to pass, the circuit of the tester becomes complete. The current flows in the liquid circuit and the bulb glows. When the liquid does not allow the electric current to pass, the circuit of the tester is not complete and the bulb does not glow.

Q. 6. There are some situations in which even though liquid is conducting, bulb may not glow. Give reasons.
Ans. The possible reasons may be:
(i) The current may be weak.
(ii) Bulb may be fused.
(iii) Incomplete circuit.
 

Q. 7. Explain why a bulb glows on passing current.
Ans. When the current passes through a bulb, the filament of the bulb gets heated to a high temperature due to the heating effect of current. The bulb starts to glow. Sometimes the current is too weak and filament does not get heated sufficiently and bulb does not glow.
 

Q. 8. What is LED? Why is it most important source of light?
Ans. The device which is used in the tester in place of bulb is called LED. It glows even at very small current. There are two wires called leads attached to the LED. One lead is longer than the other. A long wire is connected with the positive terminal and shorter lead is connected to the negative terminal of battery.

Q. 9. What do you mean by magnetic effect of electricity?
Ans. When electric current is passed through a coil or wire, then it behaves like a magnet. This is called magnetic effect of current. The strength of magnetic field depends on the amount of current passing through a coil or wire. The coil or wire shows magnetism till current is passed.
 

Q. 10. The ordinary water can conduct electricity while distilled water does not. Explain why.
Ans. The water that we get from various sources like taps, hand pumps, wells and ponds is not pure. It may contain several salts dissolved in it. This water is thus good conductor of electricity. Distilled water is free of salts due to which it is a poor conductor.
 

Q. 11. Why do we need magnetic compass to test the conduction of electric current?
Ans. Sometimes the bulb does not glow on passing electric current. This is because the electric current flowing through a conductor is so small, that the filament of the bulb does not get heated up to the temperature where it starts glowing. So, in case of small current we need magnetic compass to test the conduction. 

Q. 12. What is chemical effect of electricity? Give some examples of chemical effects.
Ans. The process in which a chemical reaction or change takes place in a solution on passing electricity is called chemical effect of electricity.
The passage of an electric current through a conducting solution causes chemical reactions. For example, change in colour of solutions and electroplating.