28/02/2023
_*Current Electricity*_
👇
💎Q.1.
*In a current carrying conductor the net charge is*
(a) 1.6 x 10–19 coulomb
(b) 6.25 x 10–18 coulomb
(c) *zero✅*
(d) infinite
*⏺️Explanation:⏺️*
*💎(In a current carrying conductor, the net charge is zero.)💎*
👇
💎Q.2.
*The current which is assumed to be flowing in a circuit from positive terminal to negative, is called*
(a) direct current
(b) pulsating current
(c) *conventional current✅*
(d) alternating current
👇
💎Q.3.
*When no current is passed through a conductor,*
(a) the free electrons 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 zero
(d) *the average of the velocities of all the free electrons at an instant is non zero✅*
👇
💎Q.4.
*A current passes through a wire of nonuniform cross-section. Which of the following quantities are independent of the cross-section?*
(a) The charge crossing
(b) Drift velocity
(c) Current density
(d) *Free-electron density✅*
👇
💎Q.5.
*In the equation AB = C, A is the current density, C is the electric field, Then B is*
(a) *resistivity✅*
(b) conductivity
(c) potential difference
(d) resistance
*⏹️Explanation:⏹️*
*💎(J =σE ⇒ Jρ=E*
*J is current density, E is electric field*
*so B = ρ = resistivity.)💎*
👇
💎Q.6.
*Drift velocity of electrons is due to*
(a) motion of conduction electrons due to random collisions.
(b) *motion of conduction electrons due to electric field E✅*
(c) repulsion to the conduction electrons due to inner electrons of ions.
(d) collision of conduction electrons with each other.
*⏺️Explanation:⏺️*
*💎(Motion of conduction electrons due to random collisions has no preffered direction and average to zero. Drift velocity is caused due to motion of conduction electrons due to applied electric field E.)💎*
👇
💎Q.7.
*The speed at which the current travels, in conductor, is nearly equal to*
(a) 3 × 104 m/so
(b) 3 × 105 m/s
(c) 4 × 106 m/s
(d) *3 × 108 m/s✅*
👇
💎Q.8.
*In the absence of an electric field, the mean velocity of free electrons in a conductor at absolute temperature (T) is*
(a) *zero✅*
(b) independent of T
(c) proportional to T
(d) proportional to T2
👇
💎Q.9.
*When a potential difference V is applied across a conductor at a temperature T, the drift velocity of electrons is proportional to*
(a) V
(b) *V✅*
(c) T
(d) T
👇
💎Q.10.
*For which of the following dependence of drift velocity vd on electric field E, is Ohm’s law obeyed?*
(a) vd α E2
(b) vd = E1/2
(c) vd = constant
(d) *vd = E✅*
👇
💎Q.11.
*The current density (number of free electrons per m3) in metallic conductor is of the order of*
(a) 1022
(b) 1024
(c) 1026
(d) *1028✅*
👇
💎Q.12.
*A current passes through a resistor. If K1 and K2 represent the average kinetic energy of the conduction electrons and the metal ions respectively then*
(a) K1 < K2
(b) K1 = K2
(c) *K1 > K2✅*
(d) any of these three may occur
👇
💎Q.13.
*A metal wire is subjected to a constant potential difference. When the temperature of the metal wire increases, the drift velocity of the electron in it*
(a) increases, thermal velocity of the electron increases
(b) *decreases, thermal velocity of the electron increases✅*
(c) increases, thermal velocity of the electron decreases
(d) decreases, thermal velocity of the electron decreases
*⏹️Explanation⏺️:*
*💎(When the temperature increases, resistance increases. As the e.m.f. applied is the same, the current density decreases the drift velocity decreases. (Contact admin 03446062703 if you wanna be added )But the rms velocity of the electron due to thermal motion is proportional to √T . The Thermal velocity increases.)💎*
👇
💎Q.14.
*The electric field intensity E, current density J and specific resistance k are related to each other through the relation*
(a) E = J/k
(b) *E = J k✅*
(c) E = k/J
(d) k = J E
👇
💎Q.15.
*The relaxation time in conductors*
(a) increases with the increases of temperature
(b) *decreases with the increases of temperature✅*
(c) it does not depends on temperature
(d) all of sudden changes at 400 K
*⏺️Explanation:⏹️*
*💎(Because as temperature increases, the resistivity increases and hence the relaxation time decreases for conductors)💎*
👇
💎Q.16.
*We are able to obtain fairly large currents in a conductor because*
(a) the electron drift speed is usually very large
(b) *the number density of free electrons is very high and this can compensate for the low values of the electron drift speed and the very small magnitude of the electron charge✅*
(c) the number density of free electrons as well as the electron drift speeds are very large and these compensate for the very small magnitude of the electron charge
(d) the very small magnitude of the electron charge has to be divided by the still smaller product of the number density and drift speed to get the electric current
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💎Q.17.
*In conductor when electrons move between two collisions, their paths are … A… when external fields are absent and … B…when external filed is present. Here, A and B refer to*
(a) straight lines, straight lines
(b) *straight lines, curved lines✅*
(c) curved lines, straight lines
(d) curved lines, curved lines
⏺️Explanation:⏹️
*💎(In conductor when electrons move between two collisions, their paths are straight lines when external fields are absent and paths are curved in general when external field is present.)💎*
👇
💎Q.18.
*The effective resistance between C & D in given circuit is*
(a) R
(b) 3R
(c) *2R/3✅*
(d) R/3
👇
💎Q.19.
*Two or more resistors are said to be in …A… if one end of all resistors is joined together and similarly the other ends joined together, Here, A refers to*
(a) series
(b) *parallel✅*
(c) either (a) or (b)
(d) None of these
👇
💎Q.20.
*The example of non-ohmic resistance is*
(a) *diode✅*
(b) copper wire
(c) filament lamp
(d) carbon resistor
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