DRIFT VELOCITY AND CURRENT
1.Two wires ‘A’ & ‘B’ are of the same metal and of the same length. Their areas of cross-sections are in the ratio of 2:1. if the same potential difference is applied across each wire in turn, what will be the ratio of the currents flowing in ‘A’ to ‘B’?
2. Explain, with the help of a graph, the variation of conductivity with temperature for a metallic conductor.
3. Draw V-I graph for ohmic and non-ohmic materials. Give one example for each.
4. Explain how does the resistivity of a metal depend upon (i) number density ‘n’ of free electrons, & (ii) relaxation time‘t’.
5. Explain how electron mobility changes for a good conductor
(i) when temperature of the conductor is decreased at constant potential difference.
(ii) applied potential difference is doubled at constant temperature.
8. Write the mathematical relation between mobility and drift velocity of charge carriers in a conductor.
Name the mobile charge carriers responsible for conduction of electric current in: (i) an electrolyte, & (ii) an ionised gas.
9. Define drift velocity. Establish a relation between current & drift velocity.
10. Define the term current density of a metallic conductor. Deduce the relation connecting current density ‘J’ & the conductivity ‘σ’ of the conductor when an electric field ‘E’ is applied to it.
Metre Bridge
write the principle of working of metre bridge. Draw a circuit diagram of a metre bridge and explain how is it used to determine the value of an unknown resistance. Why cannot such an arrangement be used for measuring very low resistance?
Calculate the value of the current drawn from a 5 V battery in the circuit as shown.
Calculate equivalent resistance of the given electrical network 
between points A and B. also calculate current through CD and AB if a 10 V d.c. source is connected between A and B. The value of R is 2 ohms.ans 2 ohm, 0A, 5A
V-I graph for a metallic wire at two different temperatures T1 and T2 is as shown in figure, which of the two temperatures is higher and why?
What is the effect of heating of a conductor on the drift velocity of free electrons and why? Ans decreases
Explain how electron mobility changes for a good conductor when (i) the temperature of the conductor is decreased at constant potential difference and (ii) applied potential difference is doubled at constant temperature. Ans i) increases, ii) no change.
Draw a graph showing variation of resistivity of copper with temperature.
Electric Power
How much power does a 60 W, 220 V bulb consume when it is operated at 110 V? Ans15 W
Two bulbs whose resistances are in the ratio of 1 : 2 are connected in parallel to a source of constant voltage. What will be the ratio of power dissipated in them? Ans 2 : 1
Two electric bulbs A and B are marked 220 V, 100 W and 220 V, 80 W respectively. Which one of the two has greater resistance? Ans B
A house hold circuit has a fuse of 5 A rating. Calculate the maximum number of bulbs of rating 60 W-240V each which can be connected in this house hold circuit. Ans 20
Two wires A and B of the same material and same length, have their cross sectional areas in the ratio 1:4. What would be the ratio of heat produced in these wires, when they are connected in series? Ans 4:1
A heater coil is rated 100 W, 200 V. It is cut in to two identical parts. Both parts are
Connected together in parallel, to the same source of 200 V. Calculate the energy liberated per second in the new combination. ans 400 W
Kirchhoff's Law
In the circuit diagram, calculate the electric current through branch BC: 
(a) 4 amp (b) 2 amp (c) 5 amp (d) 10 amp Ans. A
Electric current through resistance 10 Ω, in the given circuit is:
(a) 0 amp (b) 0.5 amp (c) 6/11 amp (d) 2 amp
Ans. C
Determine the value of current I1 in the given electric network
Answer:current I1 -1.2A
Use Kirchhoff’s rules to determine the potential
difference between the points A and D when no current flows in the arm BE of the electric network shown in the figure.
Answer: -9V
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