Electric Current
Definition
The direction of current
Charge on a current carrying conductor
Current through a conductor of non-uniform cross-section
Current in difference situation
Due to translator motion of charge
Current in difference situation
Due to rotatory motion of charge
Current in difference situation
When a voltage V applied across a resistance R
Current density (J)
Unit and dimension
Current density in terms of velocity of charge
Current density in terms of electric field
Drift velocity
Relaxation time ( )
Mobility
The potential difference applied to an X-ray tube is 5 KV and the current
through it is 3.2 mA. Then the number of electrons striking the target per
second is
(a) 2 1016
(b) 5 106
(c) 1 1017
(d) 4 1015
A beam of electrons moving at a speed of 106 m/s along a line produces a
current of 1.6 10–6 A. The number of electrons in the 1 metre of the
beam is
(a) 106
(b) 107
(c) 1013
(d) 1019
In the Bohr’s model of hydrogen atom, the electrons moves around the
nucleus in a circular orbit of a radius 5 10–11 metre. It’s time period is 1.5
10–16 sec. The current associated is
(a) Zero
(b) 1.6 10–19 A
(c) 0.17 A
(d) 1.07 10–3 A
In the Bohr’s model of hydrogen atom, the electrons moves around the
nucleus in a circular orbit of a radius 5 10–11 metre. It’s time period is 1.5
10–16 sec. The current associated is
(a) Zero
(b) 1.6 10–19 A
(c) 0.17 A
(d) 1.07 10–3 A
An electron is moving in a circular path of radius 5.1 10–11 m at a
frequency of 6.8 1015 revolution/sec. The equivalent current is
approximately
(a) 5.1 10–3 A
(b) 6.8 10–3 A
(c) 1.1 10–3 A
(d) 2.2 10–3 A
A copper wire of length 1m and radius 1mm is joined in series with an iron
wire of length 2m and radius 3mm and a current is passed through the
wire. The ratio of current densities in the copper and iron wire is
(a) 18 : 1
(b) 9 : 1
(c) 6 : 1
(d) 2 : 3
A wire has a non-uniform cross-sectional area as shown in figure. A steady
current i flows through it. Which one of the following statement is correct
(a) The drift speed of electron is constant
(b) The drift speed increases on moving from A to B
(c) The drift speed decreases on moving from A to B
(d) The drift speed varies randomly
In a wire of circular cross-section with radius r, free electrons travel with a
drift velocity v, when a current i flows through the wire. What is the
current in another wire of half the radius and of the some material when
the drift velocity is 2v
(a) 2i
(b) I
𝑖
(c)
2
𝑖
(d)
4
In a wire of circular cross-section with radius r, free electrons travel with a
drift velocity v, when a current i flows through the wire. What is the
current in another wire of half the radius and of the some material when
the drift velocity is 2v
(a) 2i
(b) I
𝑖
(c)
2
𝑖
(d)
4
A current flows in a wire of circular cross-section with the free electrons
travelling with a mean drift velocity v. If an equal current flows in a wire of
twice the radius new mean drift velocity is
(a) v
𝑣
(b)
2
𝑣
(c)
4
(d) None of these
Two wires A and B of the same material, having radii in the ratio 1 : 2 and
carry currents in the ratio 4 : 1. The ratio of drift speeds of electrons in A
and B is
(a) 16 : 1
(b) 1 : 16
(c) 1 : 4
(d) 4 : 1
