Current Electricity

Previous Years' CBSE Board Questions

3.3 Electric Currents in Conductors

V5A (1 mark)

1. How does the random motion of free electrons in a conductor get affected when a potential difference is applied across its ends? (Delhi 2014C)

3.4 Ohm's Law

6V 6V

MCQ

<math>1\Omega</math> <math>1\Omega</math>

CONTRACTOR . .......................................

9V. 9V

(1-44 11-44

<math>1\Omega</math> <math>1\Omega</math>

..... est tent t

(a) (b)

1. A potential difference of 200 V is maintained across a conductor of resistance 100 Ω. The number of electrons passing through it in 1 s is
2. <math>1.25 \times 10^{19}</math> (b) <math>2.5 \times 10^{18}</math>
3. <math>1.25 \times 10^{18}</math> (d) <math>2.5 \times 10^{16}</math> (Term | 2021-22)

(Delhi 2015C) (Ap)

1. The ratio of current density and electric field is called
2. resistivity (b) conductivity
3. drift velocity (d) mobility

OR In a current carrying conductor, the ratio of the electric field and the current density at a point is called

1. resistivity (b) conductivity
2. resistance (d) mobility

VSA (1 mark)

(Term I 2021-22) [U

1. Two wires X and Y of the same material and of equal lengths having area of cross-section A and 2A respectively, are connected in parallel across an ideal battery of emf E. What is the ratio of current density

<math>(j_x/j_y)</math> in them? (2021C)

SA II (3 marks)

1. Differentiate between electrical resistance and resistivity of a conductor. (1/3, 2020) R
2. In the two electric circuits shown in the figure, determine the readings of ideal ammeter (A) and the ideal voltmeter (V).

3.5 Drift of Electrons and the Origin of Resistivity

MCQ

If n, e, τ and m have their usual meanings, then the

resistance of a wire of length I and cross-sectional

area A is given by

mtA<br>ne²l <math>ne^2 \tau A</math> (a) The potential difference applied across a given

conductor is doubled. The mobility of the electrons

in the conductor

1. is doubled (b) is halved

1. A copper wire of non-uniform area of cross-section is connected to a d.c. battery. The physical quantity which remains constant along the wire is _____ (2020) R
2. Define the term 'electrical conductivity' of a metallic wire. Write its S.I. unit. (Al 2017C, Delhi 2014) R

SA I (2 marks)

1. A metal rod of square cross-sectional area A having length I has current I flowing through it when a potential difference of V volt is applied across its ends (figure I). Now the rod is cut parallel to its length into two identical pieces and joined as shown in figure II. What potential difference must be maintained across the length of 2/so that the current in the rod is still /?

<math>-I \longrightarrow H</math> A V

1. (11)

(Foreign 2016) (Ap)

1. Define the term 'mobility' of charge carriers in a current carrying conductor. Obtain the relation for mobility in terms of relaxation time. (2020) U

Using the concept of drift velocity of charge carriers in a conductor, deduce the relationship between current density and resistivity of the conductor. (Delhi 2015C) (Ān)

1. Estimate the average drift speed of conduction electrons in a copper wire of cross-sectional area 1.0 × 10^-7 m² carrying a current of 1.5 A. Assume the density of conduction electrons to be <math>9 \times 10^{28}</math> m^-3.

(Al 2014) I(A)

SA II (3 marks)

10 -

V_d 5

Define drift velocity of electrons in a conductor connected across a battery. Figure shows variation of the drift velocity (v_d) of electrons in two copper wires A and B of different lengths versus the potential difference (V) applied across their ends.

5 10 ▶ t(s)

(AI 2015C) [Ap]

1. What does the slope of the line represent?
2. Which one of the two wires is longer?

(2021C)

The thickness of a conductor continuously decreases from its one end (A) to another end (B). It is connected across the terminals of a battery. What will be the effect on the value of

1. electric field.
2. current density, and
3. mobility of the electron

(c)

VSA (1 mark)

How does the mobility of electrons in a conductor

change, if the potential difference applied across

the conductor is doubled, keeping the length and

temperature of the conductor constant? (2020)

How is the drift velocity in a conductor affected with

the rise in temperature? (Delhi 2019)

Define the term drift velocity of charge carriers in a

conductor and write its relationship with the current

flowing through it. (Delhi 2014)

Write the expression for the drift velocity of charge

carriers in a conductor of length 'l' across which a

potential difference 'V' is applied. (AI 2014C) [An

SAI (2 marks)

1. Define the term 'drift velocity' of electrons in a current carrying conductor. Obtain the relationship between the current density and the drift velocity of electrons. (2020)
2. A steady current flows in a metallic conductor of non- uniform cross-section. Which of these quantities is constant along the conductor : current, current density, electric field, drift speed? (1/3, Delhi 2015C)
3. (a) Deduce the relation between current I flowing through a conductor and drift velocity <math>\vec{V}_d</math> of the electrons.
4. Figure shows a plot of current 'I' flowing through the cross-section of a wire versus the time 't'. Use the plot to find the charge flowing in 10 sec through the wire.

LA (5 marks)

Define mobility of electrons. Give its SI units

(ii)