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101.	The mobility of a charge carrier is the drift velocity acquired by it in a unit cross-sectional area.(a) True(b) FalseThis question was posed to me by my school principal while I was bunking the class.This question is from Current Electricity in division Current Electricity of Physics – Class 12
Answer» CORRECT choice is (b) False The best EXPLANATION: The mobility of a CHARGE carrier is the drift velocity acquired by it in a unit ELECTRIC FIELD. Mobility=\(\frac {Drift \, velocity}{Electric \, field}\). SI unit = \(\frac {ms^{-1}}{Vm^{-1}}\) = m^2V^-1s^-1.

102.	Calculate the drift velocity of free electrons if a current of 5 A is maintained in a conductor of cross-section 10^-2m^2. The number density of free electrons is 5 × 10^20m^-3.(a) 6.25 ms^-1(b) 5.25 ms^-1(c) 2.25 ms^-1(d) 12.25 ms^-1I had been asked this question during an online interview.This interesting question is from Current Electricity topic in division Current Electricity of Physics – Class 12
Answer» Right option is (a) 6.25 ms^-1 The BEST explanation: Drift velocity = \(\FRAC {CURRENT}{(number \, density \, of \, electrons \, \times \, charge \, on \, electron \, \times \, Area)}\). \(\frac {5}{(5 \times 10^{20} \times 1.6 \times 10^{-19} \times 10^{-2})}\) = 6.25 ms^-1.

103.	Consider a conductor of length 0.5 m. A potential difference of 20V is applied across this conductor. If the drift velocity of electrons is given as 5.0 × 10^-4ms^-1, then determine the mobility of the electrons.(a) 5.25 × 10^18m^2V^-1s^-1(b) 5.25 × 10^-18m^2V^-1s^-1(c) 1.25 × 10^-5 m^2V^-1s^-1(d) 1.25 × 10^6m^2V^-1s^-1The question was asked during a job interview.My enquiry is from Current Electricity in portion Current Electricity of Physics – Class 12
Answer» Right answer is (c) 1.25 × 10^-5 m^2V^-1s^-1 The explanation: Mobility = \(\frac {DRIFT \, VELOCITY}{ELECTRIC \, field}\). Electric field = \(\frac {Voltage}{LENGTH} = \frac {20}{0.5}\) = 40Vm^-1. Mobility = \(\frac {Drift \, velocity}{Electric \, field} = \frac {5.0 \times 10^{-4}}{40}\) = 1.25 × 10^-5 m^2V^-1s^-1.

104.	In electrolytes and ionic crystals, the current carriers are free electrons.(a) True(b) FalseThe question was asked during an interview.The query is from Electric Current in chapter Current Electricity of Physics – Class 12
Answer» RIGHT choice is (b) False Easiest explanation: In electrolytes and ionic CRYSTALS, the current carriers are positive and negative ions. Whereas in most of the substances LIKE metals, the carriers of electric current are ELECTRONS.

105.	A set up is such that there are three similar resistors, each of 20 ohms resistance. Two of them are connected in parallel, and this combination is connected in series with the third one. The maximum power that can be consumed by each resistor is 30 W. Then, what is the maximum power that can be consumed by the combination of all three resistors?(a) 30(b) 20(c) 35(d) 45This question was addressed to me in an online interview.This intriguing question originated from Combination of Resistors topic in division Current Electricity of Physics – Class 12
Answer» Right answer is (d) 45 The explanation is: The EQUIVALENT overall resistance of the parallel combination is: \(\FRAC {1}{R1} = \frac {1}{20} + \frac {1}{20} = \frac {2}{20} = \frac {1}{10}\) → R1 = 10 OHMS. R1 is in series with R2; So, R3 = R1 + R2 = 10 + 20 = 30 ohms. Now, we can employ the method of cross-multiplication: For 20 ohms resistor→ 30 W power CONSUMED For 30 ohms resistor combination → x 20x = 30 × 30 x = \(\frac {30 \times 30}{20}\) x = 45 Therefore, the power consumed by the parallel combination is 45 ohms.

106.	‘X’ is a type of commercial resistor made from a mixture of clay, carbon black, and resin binder which are pressed and then molded into cylindrical rods by heating. Identify X.(a) Wire-bound resistors(b) Carbon resistors(c) Metal film resistors(d) Surface-mount resistorsThis question was posed to me in a national level competition.The doubt is from Current Electricity topic in section Current Electricity of Physics – Class 12
Answer» Right answer is (b) Carbon RESISTORS Easiest explanation: Carbon resistors are made from a mixture of carbon black, CLAY and resin binder which are pressed and then MOLDED into cylindrical rods by heating. The rods are enclosed in a CERAMIC or plastic jacket. They are used in circuits of radio receivers, AMPLIFIERS, etc.

107.	Identify the type of conductors in which both positive and negative charges can move.(a) Thermosets(b) Metallic conductors(c) Electrolytic solutions(d) PolymersThe question was posed to me in an interview for internship.My question is from Electric Currents in Conductors in section Current Electricity of Physics – Class 12
Answer» CORRECT option is (c) Electrolytic solutions For explanation: Electrolytic solutions are those that are capable of conducting an electrical CURRENT. They are generally ions, in which both positive and negative charges can move. Polymers and thermosets do not CONDUCT electric charge. Electrons are the charge CARRIERS in metallic CONDUCTORS.

108.	Identify the factor which does not depend on the resistance of a conductor.(a) Nature of material(b) Area of cross-section(c) Length(d) ViscosityI had been asked this question in semester exam.My enquiry is from Ohm’s Law in portion Current Electricity of Physics – Class 12
Answer» The correct choice is (d) Viscosity Explanation: The resistance of a CONDUCTOR is directly proportional to its LENGTH, INVERSELY proportional to the AREA of cross-section, and NATURE of the material. The resistance of the conductor does not depend on viscosity.

109.	Which of these is a correct definition of conventional current?(a) Current that flows from lower potential to higher potential(b) The current which remains static(c) Current constituted by the flow of ions(d) Current that flows from higher potential to lower potentialI got this question by my school principal while I was bunking the class.I want to ask this question from Electric Current in portion Current Electricity of Physics – Class 12
Answer» RIGHT option is (d) Current that FLOWS from higher potential to lower potential Explanation: The current that flows from a point at the higher (positive) potential to a point at lower (NEGATIVE) potential is CALLED conventional current. The DIRECTION of motion of positive charges is taken as the direction of electric current.

110.	What is the number of electrons that constitutes a current of one Ampere?(a) 2.25 × 10^18(b) 2.25 × 10^-18(c) 6.25 × 10^18(d) 6.25 × 10^-18The question was posed to me during an interview.This question is from Electric Current in section Current Electricity of Physics – Class 12
Answer» The correct option is (c) 6.25 × 10^18 Best explanation: Number of electrons, n = \(\frac {Current (I) \times time (t)}{Charge \, of \, 1 \, ELECTRON (e)}\)= \(\frac {(1 \times 1)}{1.6 \times 10^{-19}}\) = 6.25 × 10^18.

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