CBSE Guess > Papers > Important Questions > Class XII > 2011 > Physics > Physics By Mr. Ajay Sharma

CBSE CLASS XII

Current Electricity

Q.1) The current-voltage graph for a device is shown in figure. The resistance is negative in region (H)

( 1 mark )

(a) AB
(b) BC
(c) ABC
(d) BA

(Q.2) Under what condition will the strength of current in a wire of resistance R be the same for connection in series and in parallel of n identical cells each of the internal resistance r, when ( 1 mark )

(a) R = n r
(b) when R = r/n
(c) when R = r
(d) when

(Q.3) If 1 A current flows through a conductor when a potential difference of 2 volt is applied across its ends, the resistance of a conductor will be ( 1 mark )

(Q.4) The dimensions of electrical conductivity is ( 1 mark )

(a) [ M^-1L^-3T³A²]
(b) [ M^-1L^-3T^-3A²]
(c) [ M^-1L³T³A²]
(d) [ M¹L^-3T³A²]

(Q.5) Of the two bulbs in a house, one bulb glows brighter than the other. Which of the two has a larger resistance?(1 mark )

(a) Brighter bulb
(b) Dim bulb
(c) Both have same resistance
(d) The brightness of a bulb is not concerned with its resistance.

(Q.6) current of 1.344 amperes is flowing through a copper wire of 1 mm² cross section. The number of free electrons in copper per c.c. is 8.4 × 10²². The drift velocity of electrons is(H)(1mark )

(a) 1.0 cm/sec
(b) 10 cm/sec
(c) 0.1 cm/sec
(d) 0.01 cm/sec

(Q.7) Variation of current passing through a conductor as the voltage applied across its ends is varied as shown in the diagram below. If the resistance is determined at the points, A, B, C, D we will find that: (H) (Q.7) Variation of current passing through a conductor as the voltage applied across its ends is varied as shown in the diagram below. If the resistance is determined at the points, A, B, C, D we will find that: (H)

(a) Resistance at C and D are equal
(b) Resistance at B is higher than at C
(c) Resistance at C is higher than at D
(d) Resistance at A is lower than at B

(Q.8) In a Bohr’s model of hydrogen atom, the electron is pictured to rotate in a circular orbit of radius 5 × 10^–11m at a speed of 2.2 × 10⁶ m/s. What is the current associated with the electron motion ? ( 1 mark )

(a) 100 mA
(b)112 mA
(c) 9 mA
(d) 28 mA

(Q.9) If n, e, T and m denote the density, charge, time of relaxation and mass of electrons in a conductor, the resistivity is given by: ( 1 mark )

(Q.10) The resistance of a certain wire of iron is R. If its length and radius are both doubled, then ( 1 mark )

(a) The resistance and the specific resistance, will both remain unchanged
(b) The resistance will be doubled and the specific resistance will be halved
(c) The resistance will be halved and the specific resistance will remain unchanged
(d) The resistance will be halved and the specific resistance will be doubled

(Q.11) Express which of the following set ups can be used to verify Ohm’s law? ( 1 mark )

(Q.12) Null point with 1 V cell comes out to be 55 cm and with R= 10 ohm it is 50 cm. What is the internal resistance of the cell? (H)

(a) 0.5 Ω
(b) 0.4 Ω
(c) 1 Ω
(d) 0.2 Ω

(Q.13) Two resistances R₁ and R₂ are made of different materials. The temperature coefficient of the material of R₁ is a and that of material of R₂ is b. The resistance of the series combination of R₁ and R₂will not change with temperature if equals (1mark )

(Q.14) Sensitivity of a potentiometer can be increased by ( 1 mark )

(a) Increasing the e.m.f of the cell
(b) Increasing the length of the potentiometer wire
(c) Decreasing the length of the potentiometer wire
(d) Decreasing the e.m.f of the cell

(Q.15) In the experiment of potentiometer, at balance point, there is no current in the ( 1 mark)

(a) Main circuit
(b) Galvanometer circuit
(c) Potentiometer circuit
(d) Both main and galvanometer circuits

(Q.16) In the diagram below each resistance is of 1 ohm. The total resistance between A and B is(H)

(a) 7/8 ohm
(b) 3/5 ohm
(c) 8/7 ohm
(d) 7ohm

(Q.17) If in the experiment of Wheatstone bridge, the positions of cells and galvanometer are interchanged, then balance point will ( 1 mark )

(a) Change
(b) Remain unchanged
(c) Depend on the internal resistance of cell and resistance of cell and resistance of galvanometer
(d) Not be able to find

(Q.18) The current I and voltage V graph for a given metallic wire at two different temperatures T₁ and T₂ are shown in the figure. It is concluded that

(a) T₁ > T₂
(b) T₁ < T₂
(c) T₁ = T₂
(d) T₁ = 2 T₂

(Q.19) If temperature is decreased, then relaxation time of electrons in metals will ( 1 mark )

(a) Increase
(b) Decrease
(c) Fluctuate
(d) Remains constant

(Q.20) What will be the equivalent resistance between the two points A and D of figure? (H)

(a) 10 ohm
(b) 20 ohm
(c) 30 ohm
(d) 40 ohm

(Q.21) A cylindrical copper rod is reformed to twice its original length with no change in volume. The resistance between its ends before the change was R. Now its resistance will be ( 1 mark )

(a) 8R
(b) 6R
(c) 4R
(d) 2R

(Q.22) The temperature coefficient of resistance of a wire is 0.00125 ºC^–1.At 300 K its resistance is one ohm. The resistance of the wire will be 2 ohm at ( 1 mark )

(a) 1154 K
(b) 1100 K
(c) 1400 K
(d) 1127 K

(Q.23) The resistivity of a typical insulator (for example amber) is greater than that of a metal by a factor of order of ( 1 mark )

(a) 10⁴
(b) 10⁹
(c) 10²³
(d) 10^-23

(Q.24) In the absence of an electric field, the mean velocity of free electrons in a conductor at absolute temperature (T) is ( 1 mark )

(a) Zero
(b) Independent of T
(c) Proportional to T
(d) Proportional to T₂

(Q.25) The current which is assumed to be flowing in a circuit from positive terminal to negative terminal, is called ( 1 mark )

(a) Direct current
(b) Pulsating current
(c) Conventional current
(d) Alternating current

(Q.26) Identify which one is the Ohm’s law formula ( 1 mark )

(a) V = IR
(b) R = VI
(c) V = I / R
(d) P = V X I

(Q.27) When maximum current is provided by battery? ( 1 mark )

(Q.28) For a given carbon resistor, the first strip is Blue, second strip is orange third and fourth strips are green and gold respectively. What is its resistance? ( 1 mark )

(Q.29) What is the effect on drift velocity of electrons if temperature is increased? (H) (1 mark)

(Q.30) What is the working principle of a potentiometer? ( 1 mark )

(Q.31) What is the value of temperature coefficient of resistance of insulators and semi conductors? (H) ( 1 mark )

(Q.32) Two bulbs A and B are marked 220v, 40w and 220v, 60w respectively. Which one of the two has greater resistance. ( 1 mark )

(Q.33) If the radius of a copper wire is doubled, what will happen to its specific resistance? (H) ( 1 mark )

(Q.34) State two uses of potentiometer. ( 1 mark )

(Q.35) What is the current flowing through a conductor if 2 million electrons are crossing in 1 millisecond through a cross section of it? ( 1 mark )

(a) 1.6x10^-10 A
(b) 3.2x10^-5 A
(c) 3.2x10^-10 A
(d) 1.6x10^-5 A

(Q.36) If a copper wire is stretched to make it 0.1% longer. What is the percentage change in resistance? (H) ( 2 Marks )

(Q.37) What is the effective resistance of the following network ( 2 Marks )

(Q.38) Define electromotive force. ( 2 Marks )

(Q.39) Define one ohm? ( 2 Marks )

(Q.40) What is conductivity? ( 2 Marks )

(Q.41) Find the value of current in following network? (H)

( 2 Marks )

(Q.42) What are the charge carriers in ionic crystals and electrolytic liquids? (H) (2 Marks )

(Q.43) Define electric current? ( 2 Marks )

(Q.44) What is specific resistance of a conductor? ( 2 Marks )

(Q.45) What is temperature coefficient of resistivity? ( 3 Marks )

(Q.46) What is internal resistance of a cell, how is it related to current drawn from a cell?(3Marks )

(Q.47) State Kirchhoff’s laws of electricity? ( 3 Marks )

(Q.48) A battery of emf 6 v and internal resistance1 ohm is connected to a resistor.if the current in the resistor is 0.5A find the resistance of the resistor? What is the terminal voltage of the battery when the circuit is closed? ( 3 Marks )

(Q.49) Ohm’s law is not a fundamental law of nature. Justify the statement? (H) (3 Marks )

(Q.50) An electric cable of copper has just one wire of radius 9mm. Its resistance is 5 ohm . 6 different well-insulated copper wires of radius 3mm each replace this single wire of cable. What will be the total resistance of cable? ( 3 Marks )

(Q.51) A conductor of resistance 10ohm is bent in the form of a circle.What is the resistance between the points on any diameter of the circle. ( 3 Marks )

(Q.52) Resistance between the points A and B is given in the following figure, reduce the following network to get the equivalent resistance. (H)

( 5 Marks )

(Q.53) A circuit shown in the fig. has potential 6v, 3v, and 2v at points A,B and C respectively. Find the potential at point O (H)

( 5 Marks )

(Q.54) The length of a given cylindrical wire is increased by 100%. Due to the consequent decrease in diameter; find the change in the resistance of the wire. (H) ( 5 Marks )

(Q.55) What is a wheat stone bridge. Also explain its working?

 

Submitted By Mr. Ajay Sharma
Email Id : [email protected]