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Electricity

Description: CURRENT ELECTRICITY
Number of Questions: 16
Created by:
Tags: current electricity Electric Charge and Current Resistivity and Factors Affecting Resistivity Equivalent Combination of Resistances in Parallel and Series Potential and Potential Difference Factors Affecting Resistance Electric Power and Energy
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A PN junction diode is connected to a battery of emf 5.5 V and external resistance 5.1 kΩ. The barrier potential in the diode is 0.4 V. The current in the circuit is

  1. 0.07843 mA

  2. 1.07 mA

  3. 927.27 A

  4. 28050 A

  5. 12750 A

Show answer
Correct Option: B
Explanation:

Out of 5.5 volts, 0.4 volt (barrier potential) is dropped across the forward biased diode and the remaining 5.1 volts appears across the 5.1 kΩ resistance. So, the current through the resistance is (5.5 V /5.1kΩ), which is equal to 1.07 mA

The storage battery of a car has an emf of 12 V. If the internal resistance of the battery is 0.4, what is the maximum current that can be drawn from the battery?

  1. 30 A

  2. 0.033 A

  3. 48 A

  4. 4.8 A

  5. 0.33 A

Show answer
Correct Option: A
Explanation:

According to  Ohm’s law E = Ir I = E/r = 12/0.4 = 30 A

A 500 watt toaster is connected to a 120 V household outlet, then calculate the resistance of the toaster.

  1. 28.8 ohm

  2. 7200 k ohm

  3. 0.034 ohm

  4. 4.166 ohm

  5. 0.24 ohm

Show answer
Correct Option: A
Explanation:

V = 120 V P = 500 W Find: R Use the P = V2 / R equation to calculate the resistance: R = V2 / P = (120 V)2 / (500 W) R = 28.8 ohm

A battery of emf 10 V and internal resistance 3 is connected to a resistor. If the current in the circuit is 0.5 A, what is the resistance of the resistor?

  1. 5 ohm

  2. 2 ohm

  3. 17 ohm

  4. 0.05 ohm

  5. 20 ohm

Show answer
Correct Option: C
Explanation:

The relation for current using Ohm’s law is I = E / R + r R + r = E / I = 10 / 0.5 R + r = 20 ohm R = 20 - 3 R = 17 ohm

A negligibly small current is passed through a wire of length 15 m and uniform cross-section 6.0 × 10−7 m2 and its resistance is measured to be 5.0 Ω. Then calculate the resistivity of the wire.

  1. 2 × 10−7 Ω.m

  2. 450 × 10−7 Ω.m

  3. 0.5 × 10−7 Ω.m

  4. 0.5 × 107 Ω.m

  5. 18 × 107 Ω.m

Show answer
Correct Option: A
Explanation:

R = ρL/A ρ = R A / L = 5 x 6.0×10−7 / 15 = 2 ×10−7 Ω.m

If the cell is replaced by another cell, the balance point shifts to 60 cm. What is the emf of the second cell, if a potentiometer arrangement a cell of emf 1.25 V gives a balance point at 35 cm length of the wire?

  1. 1680 V

  2. 2.14 V

  3. 2625 V

  4. 0.0006 V

  5. 0.729 V

Show answer
Correct Option: B
Explanation:

E1= 1.25 V l1 = 35 cm l2 = 60 cm E1/E2 = l1/l2 E2 = l2 E1/ l1 E2 = 60 x 1.25/35 E2 = 2.14 V

Calculate the effective capacitance of the combination in series with data C1 = 10μF; C2 = 5μF.

  1. 0.3 micro F

  2. 3.33 micro F

  3. 15 micro F

  4. 0.3 mega F

  5. 0.02 mega F

Show answer
Correct Option: B
Explanation:

1/ C = 1/C1 + 1/C2 = 1/10 +1/5Cs = 10 x 5/ 10 + 5 = 3.33 micro F

Calculate how many joules of energy will a 20 W lamp dissipate in one minute.

  1. 1200 J

  2. 20 J

  3. 0.33 J

  4. 3 J

  5. 0.05 J

Show answer
Correct Option: A
Explanation:

Power = Joules/time. Joules = Power*time J = 20* 60 (1 min = 60 sec) Joules = 1200

If a current of 10 mA passes through your cell phone battery charger wire for 10 minutes, what quantity of electric charge is transferred through the wire to the battery?

  1. 6 C

  2. 0.000016 C

  3. 60000 C

  4. 1000 C

  5. 0.001 C

Show answer
Correct Option: A
Explanation:

∆Q = I×∆t ∆Q = (10*10-3) * (10 * 60 s) = 6 C

What is a resistor whose value of resistance depends on its temperature known as?

  1. LDR

  2. Strain guage

  3. Thermistor

  4. Preset

  5. VDR

Show answer
Correct Option: C
Explanation:

A thermistor is a type of resistor whose resistance varies significantly with temperature, more so than in standard resistors.

In which form does the capacitor store energy within a dielectric between the conducting plates?

  1. Magnetic field

  2. Electric field

  3. Electromagnetic field

  4. Positive voltage

  5. Negative voltage

Show answer
Correct Option: B
Explanation:

Capacitor always stores energy in the form of electric field.

Three 3 ohm resistors are connected to form a triangle. The resistance between any two corners is

  1. 0.5 ohm

  2. 0.055 ohm

  3. 0.11 ohm

  4. 18 ohm

  5. 9 ohm

Show answer
Correct Option: A
Explanation:

Resistance between any two corners =R, and 1/R =1/3+1/(3+3) =1/3 + 1/6 =9/18 R =1/2 =0.5 ohm

Calculate the rate at which heat is developed in the heater, if it has resistance 8 ohm and 15 ampere current passes through it for 2 hours.

  1. 3600 J

  2. 900 J

  3. 0.0011 J

  4. 0.016 J

  5. 60 J

Show answer
Correct Option: A
Explanation:

R = 8 ohmI = 15 AT = 2 hrH = I2RTH = 152 x 8 x 2H = 3600 J

Calculate the current flowing through the wire of charge 20 C when the time is 40 seconds.

  1. 0.50 Ampere

  2. 2 Ampere

  3. 800 Ampere

  4. 4 m Ampere

  5. 1 m Ampere

Show answer
Correct Option: A
Explanation:

I = Q / t = 20 / 40 = 0.5 Ampere

An electric locomotive has a maximum mechanical output of 4.0 MW. Electrical power is delivered at 25 kV from overhead wires. The overall efficiency of the locomotive in converting electrical power to mechanical power is 80%. What is the current from overhead wires, when locomotive is operating at its maximum power?

  1. 200 A

  2. 5 mA

  3. 6.25 mA

  4. 160 A

  5. 0.16 A

Show answer
Correct Option: A
Explanation:

With 80percent efficiency the power supplied is 4.0/0.8 Megawatts = 5Megawatts Electrical power = volts*amps 5*(106) = 25*(103)amps amps = 5 x 106/25(103) = 200amps Current drawn from overhead wires is 200amps

A conductor has a constant current of 5 A. How many electrons pass through a cross-section of the conductor in 3 minutes?

  1. 9.375 × 1019

  2. 1440 × 10-19 electrons

  3. 5.625 × 1021

  4. 0.106 × 10-19 electrons

  5. 24 × 10-19 electrons

Show answer
Correct Option: C
Explanation:

A single electron charge is q = 1.6 × 10-19C If N electrons pass through the conductor, the total charge transferred: ∆Q = N×q. If the time needed for the charge to pass through is ∆t, then the current is:I =∆Q/∆t = N×q/∆t; From this, the number of electrons: N = I×∆t/q. ∆t = 3 min. = 3×60 s = 180 s. N = 5 A×180s/ 1.6×10-19C = 5.625×1021electrons Answer: N = 5.625×1021electrons

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