10 Question-answer on electric current
1. Constant current is flowing through a linear conductor of non-uniform area of cross-section. The charge flowing per second through the area of conductor at any cross-section is:
(a) Proportional to the area of cross section
(b) Inversely proportional to the area of cross section
(c) Independent of the area of cross section
(d) Dependent on the length of conductor.
Ans: (c)
2. When the current I is flowing through a conductor, the drift velocity is v. if 2i current is flowed through the same metal but having double the area of cross-section, then the drift velocity will be:
(a) v
(b) v/2
(c) v/4
(d) 4v
Ans: (a)
3. When the electric current through a conducting wire along its length, then an electric field must exist
(a) Outside the wire but parallel to it
(b) Outside the wire but perpendicular to it
(c) inside the wire but parallel to it
(d) inside the wire but perpendicular to it
Ans : ( c)
4. A metallic resistor is connected across a battery. If the number of collisions of the free electrons with the lattice is somehow decreased in the resistor ( foe example by cooling it), the current will
(a) Remains constant
(b) Increase
(c) Decrease
(d) Become zero
Ans: (b)
5. When no current is passed through a conductor:
(a) The free electron do not move
(b) The average speed of a free electron over a large period of time is not zero
(c) The average velocity of a free electron over a large period of time is not zero
(d) The average of velocities of all the free electron at the instant is zero
Ans: ( c, d)
6. A current passes through a wire of non uniform cross-section. Which of the following quantities are independent of cross-section?
(a) Drift speed
(b) Current density
(c) Free electron density
(d) The charge crossing in a given time interval
Ans: (c,d)
7. Which of the following characteristics of electron determines the current in a conductor?
(a) Thermal velocity alone
(b) Drift velocity alone
(c) Both thermal velocity and drift velocity
(d) None of above
Ans: (b)
8. A current of 5A exist in a 10 Ω resistance for 4 minutes. How many coulombs pass through any cross-section of the resistor in this time?
(a) 12 C
(b) 120 C
(c) 1200 C
(d) 12000 C
Ans: ( c)
9. A metallic block has no potential difference applied across it, then the mean velocity of free electrons at absolute temperature T is:
(a) Proportional to T
(b) Proportional to √T
(c) Zero
(d) Finite but independent of T.
Ans: ( c)
10. Current flows through a metallic conductor whose area of cross-section increases in the direction of the current. If we move in this direction,
(a) The current density will change
(b) The current will change
(c) The drift velocity will decreases
(d) The drift velocity will increases
Ans: ( c)