Current Electricity (Part - 1) - Physics, Solution by DC Pandey NEET Notes | EduRev

DC Pandey (Questions & Solutions) of Physics: NEET

Created by: Ciel Knowledge

NEET : Current Electricity (Part - 1) - Physics, Solution by DC Pandey NEET Notes | EduRev

The document Current Electricity (Part - 1) - Physics, Solution by DC Pandey NEET Notes | EduRev is a part of the NEET Course DC Pandey (Questions & Solutions) of Physics: NEET.
All you need of NEET at this link: NEET

INTRODUCTORY EXERCISE 20.1
Ques 1: In the Bohr model of hydrogen atom, the electron is pictured to rotate in a circular orbit of radius 5 × 10-11 m, at a speed 2.2 × 106 m/s. What is the current associated with electron motion?
Ans: 
Current Electricity (Part - 1) - Physics, Solution by DC Pandey NEET Notes | EduRev
Current Electricity (Part - 1) - Physics, Solution by DC Pandey NEET Notes | EduRev
= 1.12 × 10-3A = 1.12mA

Ques 2: Copper has one conduction electron per atom. Its density is 8.89 g/cm3 and its atomic mass is 63.54 g/mol. If a copper wire of diameter 1.0 mm carries a current of 2.0 A. What is the drift speed of the electrons in the wire?
Ans:
ρ = 8.89 × 103 kg/m3
Mass of 1 m3 = 8.89 × 103 kg= 8.89 × 103 kg
∴ Number of gram moles
Current Electricity (Part - 1) - Physics, Solution by DC Pandey NEET Notes | EduRev
Number of atoms = 1.4 × 105 × 6.02 × 1023
= 8.42 × 1028
One atom emits one conduction electron. Therefore number of free electrons in unit volume (or lm3 volume)
n = 8.42 × 1028 per m3
Now i = neA vd
Current Electricity (Part - 1) - Physics, Solution by DC Pandey NEET Notes | EduRev
Current Electricity (Part - 1) - Physics, Solution by DC Pandey NEET Notes | EduRev
= 1.9 × 10-4m/s

Ques 3: When a steady current passes through a cylindrical conductor, is there an electric field inside the conductor?
Ans: Under electrostatic conditions (when no current flows), E = 0. When current is non-zero, then electric field is also non-zero.

Ques 4: Electrons in a conductor have no motion in the absence of a potential difference across it. Is this statement true or false?
Ans: False, there is random or thermal motion of free electrons in the absence of potential difference.

Ques 5: In an electrolyte, the positive ions move from left to right and the negative ions from right to left. Is there a net current? If yes, in what direction?
Ans: 
Current due to both is from left to right. So, the two current are additive.

Ques 6: The current through a wire depends on time as, i = (10 + 4t)
Here, i is in ampere and t in seconds. Find the charge crossed through a section in time interval between t = 0 to t = 10 s.

Ans: The resistance of a copper wire and an iron wire at 20°C are 4.1 Ω. and 3.9 Ω respectively. Neglecting any thermal expansion, find the temperature at which resistances of both are equal.
Current Electricity (Part - 1) - Physics, Solution by DC Pandey NEET Notes | EduRev 

INTRODUCTORY EXERCISE 20.2
Ques 1: In household wiring, copper wire 2.05 mm in diameter is often used. Find the resistance of a 35.0 m long wire. Specific resistance of copper is 1.72 ×10-8 Ω-m.
Ans: Current Electricity (Part - 1) - Physics, Solution by DC Pandey NEET Notes | EduRev
= 0.18 Ω

Ques 2: An aluminium wire carrying a current has diameter 0.84 mm. The electric field in the wire is 0.49 V/m. What is,
(a) the current carried by the wire?
(b) the potential difference between two points in the wire 12.0 m apart?
(c) the resistance of a 12.0 m length of this wire? Specific resistance of aluminium is 2.75 × 10-8 Ω-m.
Ans: 
(a) In 1 m, potentials difference,
V = 0.49
V = iR
Current Electricity (Part - 1) - Physics, Solution by DC Pandey NEET Notes | EduRev
Current Electricity (Part - 1) - Physics, Solution by DC Pandey NEET Notes | EduRev
= 9.9 A
(b) PD between two points, 12 m apart = (0.49 V/m) (12m) = 5.88 V
Current Electricity (Part - 1) - Physics, Solution by DC Pandey NEET Notes | EduRev
Current Electricity (Part - 1) - Physics, Solution by DC Pandey NEET Notes | EduRev

Ques 3: A conductor of length l has a non-uniform cross-sect ion. The radius of cross-sect ion varies linearly from a to b. The resistivity of the material is ρ. Find the resistance of the conductor across its ends.
Current Electricity (Part - 1) - Physics, Solution by DC Pandey NEET Notes | EduRev
Ans: 
Radius at distance x from end P,
Current Electricity (Part - 1) - Physics, Solution by DC Pandey NEET Notes | EduRev
Current Electricity (Part - 1) - Physics, Solution by DC Pandey NEET Notes | EduRev
Resistance of element of thickness dx is
Current Electricity (Part - 1) - Physics, Solution by DC Pandey NEET Notes | EduRevCurrent Electricity (Part - 1) - Physics, Solution by DC Pandey NEET Notes | EduRev
Current Electricity (Part - 1) - Physics, Solution by DC Pandey NEET Notes | EduRev

Ques 4: The product of resistivity and conductivity of a conductor is constant. Is this statement true or false?
Ans: 
Current Electricity (Part - 1) - Physics, Solution by DC Pandey NEET Notes | EduRev
ρσ = constant

Ques 5: The resistance of a copper wire and an iron wire at 20°C are 4.1 Ω. and 3.9 Ω respectively. Neglecting any thermal expansion, find the temperature at which resistances of both are equal.
αCu = 4.0 × 10-3K-1. and αFe= 5.0 × 10-3 K-1.
Ans: 
4.1[1 + 4.0 × 10-3(θ - 20)]
= 3.9[1 + 5.0 × 10-3(θ - 20)]
Solving we get,
θ = 85°C

INTRODUCTORY EXERCISE 20.3
Ques 1: Find the current through 2Ω and 4Ω resistance.
Current Electricity (Part - 1) - Physics, Solution by DC Pandey NEET Notes | EduRev
Ans: 
PD across each resistance is 10V.
Current Electricity (Part - 1) - Physics, Solution by DC Pandey NEET Notes | EduRev

Ques 2: In the circuit shown in figure, find the potentials of A, B, C and D and the current through 1Ω and 2Ω resistance.
Current Electricity (Part - 1) - Physics, Solution by DC Pandey NEET Notes | EduRev
Ans: 
VA = 0V (as it is earthed)
V- VA = 5W
KC = 5V V- VA = 2V
VB = 2V V- VC = 10V
V= 10 + VC = 15 V
Current Electricity (Part - 1) - Physics, Solution by DC Pandey NEET Notes | EduRev= 3A from C to B as K> K
Current Electricity (Part - 1) - Physics, Solution by DC Pandey NEET Notes | EduRev = 7.5A from D to A as VD > VA

Ques 3: For what value of E the potential of A is equal to the potential of B?
Current Electricity (Part - 1) - Physics, Solution by DC Pandey NEET Notes | EduRev
Ans: 
FA = FB
VAB = 0 or E - ir = 0
Current Electricity (Part - 1) - Physics, Solution by DC Pandey NEET Notes | EduRev
Solving this equation we get E = 5V

Ques 4: Ten cells each of emf 1V and internal resistance 1Ω. are connected in series. In this arrangement polarity of two cells is reversed and the system is connected to an external resistance of 2Ω . Find the current in the circuit.
Ans: 
Net emf = (n - 2m)E
= (10 - 2 × 2) (1) = 6 V
Current Electricity (Part - 1) - Physics, Solution by DC Pandey NEET Notes | EduRev

Ques 5: In the circuit shown in figure, R1 = R2 = R3 = 10Ω. Find the currents through R1 and R2
Current Electricity (Part - 1) - Physics, Solution by DC Pandey NEET Notes | EduRev
Ans:

Current Electricity (Part - 1) - Physics, Solution by DC Pandey NEET Notes | EduRev 

Ques 6: Draw:
(a) current versus load, and
(b) current versus potential difference graph for a cell.
Ans: (a) Current Electricity (Part - 1) - Physics, Solution by DC Pandey NEET Notes | EduRev
i versus R graph is shown in answer.
Current Electricity (Part - 1) - Physics, Solution by DC Pandey NEET Notes | EduRev
(b) V =E - ir
V versus i graph is shown in answer

Current Electricity (Part - 1) - Physics, Solution by DC Pandey NEET Notes | EduRev

Offer running on EduRev: Apply code STAYHOME200 to get INR 200 off on our premium plan EduRev Infinity!

Complete Syllabus of NEET

Dynamic Test

Content Category

Related Searches

video lectures

,

Current Electricity (Part - 1) - Physics

,

Sample Paper

,

Free

,

MCQs

,

Previous Year Questions with Solutions

,

mock tests for examination

,

pdf

,

Solution by DC Pandey NEET Notes | EduRev

,

Solution by DC Pandey NEET Notes | EduRev

,

Current Electricity (Part - 1) - Physics

,

past year papers

,

Objective type Questions

,

Important questions

,

study material

,

Solution by DC Pandey NEET Notes | EduRev

,

Viva Questions

,

practice quizzes

,

Extra Questions

,

ppt

,

shortcuts and tricks

,

Semester Notes

,

Current Electricity (Part - 1) - Physics

,

Exam

,

Summary

;