 DC Circuit | Old is Gold XII |

Short Questions

1.      An ammeter is always connected in series. Why?
2.      Why do we use connecting wires made of copper?
3.      What are the factors on which the resistance of a conductor depends?
4.      Can the potential difference across a battery be greater than its emf?
5.      Two bulbs of 60 W and 100 W are connected in series and this combination is connected across the mains.                    Which bulb will glow more brightly? Give reason.
6.      You are given n wires each of resistance rΩ. What is the ratio of maximum to minimum resistance that can be              obtained from these wires?
7.      Is terminal p.d. always connected in parallel with the load resistance?
8.      Two bulbs have the filament of the same length. If one is of 40 watt and the other 60 watt, which one has                        thicker filament?
9.      Two bulbs have the filament of the same length. If one is of 40 watt and the other 60 watt, which one has                        thicker filament?
10.  Why are alloys constantan and manganin used to make standard resistors?
11.   A large number of free electrons are present in metals. Why is there no current in the absence of electric field               across it?
12.  Explain the significance of a shut with a diagram.
13.  The element of heater is very hot while the wire carrying current are cold, why?
14.  You  are given 2 wires each of resistance R. What is the ratio of maximum to minimum resistance that can be               obtained from these wires?
15.  Why heat is generated across a resistor when the electric field is applied?
16.  Why do electric acquire a steady drift velocity?
17.  Why ammeter is always connected in series?
18.  A wire is stretched to double its length. What happens to its resistance?
19.  The energy that can be extracted from a storage battery is always less than the energy that goes into it while                  charging. Why?
20.  The resistance of an ammeter must essentially be very small. Why?
21.  Water boils in an electric kettle in 15 after being switched on. Using the same main supply. Should the length of            the heating element be increased or decreased if the water is to boil in 10 minutes? Explain.
22.  What is the ratio of maximum to minimum resistance obtained from n wires of resistance R each?
23.  Why is it essential that the resistance of a voltmeter be very high?
24.  An ammeter is always connected in series. Why?
25.  Distinguish between resistance and resistivity of a material.
26.  Long-distance, electric power, transmission lines always operate at very high voltage, some time as much as 750          kV. What are the advantages of such high voltage?
27.  Distinguish between resistance and resistivity. Derive expressions for the effective resistance of number of                    resistors connected in series and parallel.

Long Questions

1.      Deduce an expression for the heat developed in a wire by the passage of an electric current.
2.      What do you mean by a shunt? Describe its use in converting a galvanometer into an ammeter.
3.      What is drift velocity of an electron? Derive a relation between the current through a metallic conductor and                 the drift velocity in terms of the number of free electrons per unit volume of the conductor.
4.      Discuss the mechanism of metallic conduction. Derive j=new where j is the current density, e is the electronic             charge and v is drift velocity.
5.      State and explain joule`s laws of electric current. Discuss how they are verified experimentally.
6.      What do you meant by shunt? How will you convert a galvanometer into an ammeter?
7.      State and explain Ohm`s law. Two resistors are connected in parallel and third resistor be connected in series             with the combination of parallel resistors. If this combination be connected with a battery of the negligible                   internal resistance, find the potential difference across each resistor.
8.      What is meant by a shunt? How will you convert a galvanometer into a ammeter?
9.      Discuss the mechanism of metallic conduction. Derive a relation between current density and drift velocity.