Very Short Answer Questions
1. Mention the factor that maintains the flow of charge through a conductor.
Ans. Potential difference across the ends of the conductor.
2. What is meant by potential difference between two points ?
Ans. Work done per unit charge in moving a unit positive charge from one point to another point in an electric field is called potential difference between points.
3. How is the direction of electric current related to the direction of flow of electrons in a wire?
Ans. The direction of electric current in a wire is just opposite to the direction of flow of electrons in the wire.
4. What is the S.I unit of electric potential difference.
Ans. Volt.
5. Name the instrument used to measure the electric potential difference.
Ans. Voltmeter.
6. Define ohm's law.
Ans. Ohm's law states that the electric current flowing through a conductor is directly proportional to the potential difference across the ends of the conductor, provided the temperature and other physical conditions of the conductor remain the same.
7. State SI unit of resistance.
Ans. ohm.
8. Define 1 ohm resistance.
Ans. The resistance of a conductor is said to be 1 ohm if a potential difference of 1 V across the ends of the conductor makes a current of 1 A to flow through the origin and has constant slope.
9. State SI unit of resistivity.
Ans. ohm-metre.
10. What is electrical resistivity ?
Ans. Electrical resistivity of a material is defined as the resistance of the object (made of the material) of unit length and unit area of cross-section.
11. A wire of resistivity 'P' is pulled to doubled its length. What will be its new resistivity ?
Ans. New resistivity will also 'P' because resistivity of a wire does not depend on its length.
12. What happens to resistance of a conductor when temperature is increased ?
Ans. Resistance of a conductor increases with the increase in temperature.
13. State SI unit of electric power.
Ans. Volt x ampere (or Watt).
14. Name the physical quatity expressed as the product of potential difference and electric current.
Ans. Electric power.
15. What is the commercial unit of energy ?
Ans. Kilowatt hour (kWh).
5. List two distinguishing features between the resistance and resistivity of a conductor.
Ans. (i) Resistance of a conductor depends on the lenth and are of cross-section of the conductor. On the other hand, resistivity of a conductor is independent of length and area of cross-section of the conductor.
(ii) Unit of resistance is ohm. Unit of resistivity is ohm-metre.
11. A wire of resistivity 'P' is pulled to doubled its length. What will be its new resistivity ?
Ans. New resistivity will also 'P' because resistivity of a wire does not depend on its length.
12. What happens to resistance of a conductor when temperature is increased ?
Ans. Resistance of a conductor increases with the increase in temperature.
13. State SI unit of electric power.
Ans. Volt x ampere (or Watt).
14. Name the physical quatity expressed as the product of potential difference and electric current.
Ans. Electric power.
15. What is the commercial unit of energy ?
Ans. Kilowatt hour (kWh).
Short Answer Questions
1. Define electric current. State and define its SI unit.
Ans. Electric current is defined as the amount of charge flowing through a cross-section of a conductor in unit time.
Charge Q
I = Time = t .
SI unit of electric current is ampere (A).
Electric current through a conductor is said to be 1 ampere if one coulomb charge flows through a cross-section of the conductor in one second.
2. List two reasons why nichrome is used for making heating element of electrical appliances.
Ans. It should be made of nichrome wire because
(i) resistivity of nichrome is greater that that of iron and silver, so more heat is produced in the nichrome wire due to the flow of current.
(ii) melting point of nichrome wire is greater than that of iron and silver and hence it does not melt easily on heating.
(iii) nichrome wire does not oxidise (or burn) easily even at higher temperature.
3. Why is Tungsten used for the filament in electric bulb?
Ans. This is because (i) melting point of tungsten is very high (about 3380 C) and (ii) it does not oxidise (or burn) even at higher temperatures.
4. (a) Why an ammeter likely to burn out if you connect it in parallel ?
(b) Why is series arrangement not found satisfactory for domestic lights ?
Ans. (a) Ammeter is a low resistance device. If it is connected in parallel, a large current flows through it. Hence, large heat is produced and it may burn the ammeter.
(b) If domestic lights are connected in series, then all lights are switched off even when only one light fuses.2. List two reasons why nichrome is used for making heating element of electrical appliances.
Ans. It should be made of nichrome wire because
(i) resistivity of nichrome is greater that that of iron and silver, so more heat is produced in the nichrome wire due to the flow of current.
(ii) melting point of nichrome wire is greater than that of iron and silver and hence it does not melt easily on heating.
(iii) nichrome wire does not oxidise (or burn) easily even at higher temperature.
3. Why is Tungsten used for the filament in electric bulb?
Ans. This is because (i) melting point of tungsten is very high (about 3380 C) and (ii) it does not oxidise (or burn) even at higher temperatures.
4. (a) Why an ammeter likely to burn out if you connect it in parallel ?
(b) Why is series arrangement not found satisfactory for domestic lights ?
Ans. (a) Ammeter is a low resistance device. If it is connected in parallel, a large current flows through it. Hence, large heat is produced and it may burn the ammeter.
5. List two distinguishing features between the resistance and resistivity of a conductor.
Ans. (i) Resistance of a conductor depends on the lenth and are of cross-section of the conductor. On the other hand, resistivity of a conductor is independent of length and area of cross-section of the conductor.
(ii) Unit of resistance is ohm. Unit of resistivity is ohm-metre.
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