01:- In Bohr’s model of hydrogen atom an electron revolves with a frequency 7x 1015Hz in a circular path of radius 0.51 Å . What is equivalent current?
02:- An electron beam contains 17 no of electrons and pass through an area of 1 mm2 in 1s. Find the current density.
03:- Calculate the electric field in a copper wire of cross-section 3mm2 carrying a current of 2 amp. Conductivity of copper is 6.25 x 107 S/m.
04:- A copper wire resistance of 1OΩ and an area of cross-section 1mm2. A potential difference of 10V across the wire. calculate the average drift speed of free electrons if no of free electron/m3 = 1028.
05:- A 100 watt heater coil is used with a 200V potential difference. Find the resistance of the coil.’
06:- Current I = (2 + 4 t) A where t is in seconds, is flowing through a wire for 2 seconds. Find out amount of charge flown through the wire.
07:- An e– revolving on a circular track of radius 1.6 cm with a constant speed of 3.14 × 106 m/s. Find out the current flowing in the circle.
08:- A current 𝑰 flows through a uniform wire of diameter d then the electrons drift velocity is v. The same current will flow through a wire of diameter d/2 made of the same material, the drift velocity of the electrons in second wire is ————
09:- The number of free e– per 10 mm of an ordinary copper wire is 2 × 1021. The avg. drift speed of e– is 0.25 mm/ sec. Calculate the current flow in the wire.
10:- Two wires each of radius of cross-section r but of different materials are connected together end to end (in series). If the densities of charge carriers in the two wires are in the ratio 1 : 4, the drift velocity of electrons in the two wires will be in the ratio : ______________
11:- Three copper wires have their lengths in the ratio 5 : 3 : 1 and their masses are in the ratio 1 : 3 : 5. Their electrical resistance will be in the ratio
(1) 5 : 3 : 1
(2) 1 : 3 : 5
(3) 125 : 15 : 1
(4) 1 : 15 : 125
12:- A wire is stretched by 30% of its original. Find % increase in resistance
13:- A wire is stretched so that its radius is decreased by 3%. Find % change in its resistance.
14:- A wire is stretched by 0.02% of its original. Find % increase in resistance.
15:- There are 𝟖. 𝟒 × 𝟏𝟎𝟐𝟐 free electrons per 𝒄𝒎𝟑 in copper. The current in the wire is 0.21 A (e = 1.6× 𝟏𝟎–𝟏𝟗 C). Then the drifts velocity of electrons in a copper wire of 𝟏𝒎𝒎𝟐 cross section, will be :– _______________