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## Thursday, 28 January 2021

### CBSE Class 12 Physics - MCQ and Online Tests - Unit 3 - Current Electricity

#### CBSE Class 12 Physics – MCQ and Online Tests – Unit 3 – Current Electricity

Every year CBSE conducts board exams for 12th standard. These exams are very competitive to all the students. So our website provides online tests for all the 12th subjects. These tests are also very effective and useful for those who preparing for competitive exams like NEET, JEE, CA etc. It can boost their preparation level and confidence level by attempting these chapter wise online tests.

These online tests are based on latest CBSE Class 12 syllabus. While attempting these our students can identify the weak lessons and continuously practice those lessons for attaining high marks. It also helps to revise the NCERT textbooks thoroughly.

#### CBSE Class 12 Physics – MCQ and Online Tests – Unit 3 – Current Electricity

Question 1.
Two wires of copper are of the same length but’have different diameters. When they are connected in series across a battery, the heat generated is H1 When connected in parallel across the same battery, the heat generated during the same time is H2 Then :
(a) H1 = H2
(b) H1 < H2
(c) H1 > H2
(d) H1 > H2

Question 2.
The example of a non-ohmic resistance is:
(a) copper wire
(b) fi lament lamp
(c) carbon resistor
(d) diode

Question 3.
The specific resistance of a rod of copper as compared to that of thin wire of copper is :
(a) less
(b) more
(c) same
(d) depends upon the length and area of cross-section of the wire

Question 4.
A wire of resistance 3 Ω is cut into three pieces, which are then joined to form a triangle. The equivalent resistance between any corners of the triangle is :
(a) $$\frac{2}{3}$$ Ω
(b) $$\frac{3}{2}$$ Ω
(c) $$\frac{1}{2}$$ Ω
(d) $$\frac{1}{3}$$ Ω

Answer: (a) $$\frac{2}{3}$$ Ω

Question 5.
The length of a conductor is halved. Its resistance will be :
(a) halved
(b) doubled
(c) unchanged

Question 6.
If a certain piece of copper is to be shaped into a conductor of minimum resistance, its length (L) and cross-sectional area (a) shall respectively be :
(a) L, 2A
(b) $$\frac{L}{2}$$, 2A
(c) 2L, 2A
(d) 2l, $$\frac{A}{2}$$

Answer: (b) $$\frac{L}{2}$$, 2A

Question 7.
Given three equal resistors, how many different combinations (taken all of them together) can be made?
(a) 3
(b) 4
(c) 5
(d) 6

Question 8.
Siemen is the unit of:
(a) resistance
(b) conductance
(c) specific conductance
(d) None of these

Question 9.
The speed at which tjie current travels in a conductor is nearly:
(a) 3 × 104 ms-1
(b) 3 × 106 ms-1
(c) 3 × 108 ms-1
(d) 3 × 1010 ms-1

Answer: (a) 3 × 104 ms-1

Question 10.
In the above question, the conductance:
(a) halved
(b) doubled
(c) unchanged

Question 11.
Specific resistance of ali metals is mostly affected by:
(a) temperature
(b) pressure
(c) magnetic field
(d) volume

Question 12.
How much electric energy is consumed by a 100 W lamp used for 6 hours everyday for 30 days?
(a) 18 kJ
(b) 18 kWh
(c) 1.8 J
(d) None of these

Question 13.
How many different resistances are possible with two equal resistors?
(a) 2
(b) 3
(c) 4
(d) 5

Question 14.
The number of electrons that constitute 1 A of current is:
(a) 6.25 × 1016
(b) 6.25 × 1017
(c) 6.25 × 1018
(d) 6.25 × 1019

Question 15.
Suppose H1 is the heat generated per second in the filament of a 100 W, 250 V lamp and H2 is the heat generated in the filament of a 200 W, 250 V lamp. Then H1/H2 is equal to:
(a) 1
(b) 2
(c) $$\frac{1}{2}$$
(d) $$\frac{1}{4}$$

Answer: (c) $$\frac{1}{2}$$

Question 16.
Kirchhoffs first and second laws for electrical circuits are consequences of:
(a) conservation of energy
(b) conservation of electrical charge and energy respectively
(c) conservation of electric charge
(d) neither conservation of energy nor electric charge

Answer: (b) conservation of electrical charge and energy respectively

Question 17.
A potential difference of 10 V is applied across a conductance of 2 S. The current in the conductor will be :
(a) 20 A
(b) 5 A
(c) 0.2 A
(d) None of these

Question 18.
The length and radius of an electric resistance of a certain wire are doubled simultaneously, then the:
(a) resistance will be doubled and specific resistance will be halved
(b) resistance will be halved and specific resistance will remain uncharged
(c) resistance will be halved and the specific resistance will be doubled
(d) resistance and specific resistance will both remain uncharged

Answer: (b) resistance will be halved and specific resistance will remain uncharged

Question 19.
A galvanometer acting as a volt meter will have with its coil.
(a) a high resistance in parallel
(b) a high resistance in series
(c) a low resistance in parallel
(d) a low resistance in series

Answer: (b) a high resistance in series

Question 20.
When three identical bulbs of 60 W, 200 V rating are connected in series to a 200 V supply, the power drawn by them will be:
(a) 20 W
(b) 60 W
(c) 180 W
(d) 10 W

Question 21.
n resistances, each of R Ω, are connected in parallel gives an equivalent resistance of R Ω. If these resistances were , connected in series, the combination would have a resistance in Ω is equal to
(a) n²R
(b) R/n²
(c) R/n
(d) nR

Question 22.
In questions 135, w hen the wires are connected in series, the heat produced in the thinner wire is H1 and that in the thicker wire is H2. Then :
(a) H1 = H2
(b)H1 < H2
(c) H1 > H2
(d) H1 > H2

Question 23.
The resistance of a human body is about:
(a) 12 Ω
(b) 120 Ω
(c) 12 KΩ
(d) 120 MΩ

Question 24.
Why is the Wheatstone bridge more accurate than other methods of measuring resistances: ‘
(a) It is a null method
(b) It is based on Kirchhoffs laws
(c) It has four resistances
(d) It does not involve ohm’s law

Answer: (a) It is a null method

Question 25.
A 5 A fuse wire can with stand a maximum power of 1 W in circuit. The resistance of the fuse wire is:
(a) 0.2 Ω
(b) 5 Ω
(c) 0.4 Ω
(d) 0.04 Ω