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Electricity

Description: current electricity
Number of Questions: 15
Created by:
Tags: current electricity Electric Charge & Current Potential & Potential Difference Resistivity and Factors Affecting Resistivity Factors Affecting Resistance Equivalent Combination of Resistances in Parallel and Series Electric Power and Energy Heterotrophic Nutrition in Plants Nutrition and its Modes in Plants Photosynthesis
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Electric current is obtained from which part of an atom?

  1. Nucleus

  2. Negatively charged electrons

  3. Ionic compounds

  4. Positively charged protons

  5. Neutrons

Show answer
Correct Option: B
Explanation:

Electrons are negatively charged. So it would be overall negative, not positive. It would be a negative ion.

Why does current flow more easily through a thick wire than a thin wire of the same material which is connected at a source?

  1. Resistance is inversely proportional to the area of cross-section

  2. Resistance is inversely proportional to length

  3. Resistance is directly proportional to the area of cross-section

  4. Thin wire has a larger diameter

  5. Thin wire has more capacity for the flow of electrons

Show answer
Correct Option: A
Explanation:

The current will flow more easily through a thick wire as compared to a thin wire because the resistance of the thick wire is less than that of the thin wire. Hence less resistance will allow more current to flow.

Which of the following is true of electrical forces?

  1. Electric lines of force pass through a conductor.

  2. Electric lines of force exert lateral pressure to represent attraction between two like charges.

  3. Electrical lines of forces are produced by electrical charges.

  4. Electric lines of forces are parallel to the surface of a positively or negatively charged body.

  5. Electrical forces are weaker than gravitational forces.

Show answer
Correct Option: C
Explanation:

An electric field is produced by electric charges and interaction. The electric fields are regions where invisible lines of force produced by the presence of electric charge or potential is experienced or measured.

What will be the resistance of a circuit when the connected battery will be of 1.5 V and the passing current is 15 A?

  1. 0.1 Ω

  2. 10 Ω

  3. 22.5 Ω

  4. 6.66 Ω

  5. 33.75 Ω

Show answer
Correct Option: A
Explanation:

i = V/R 15 = 1.5/R R = 0.1 Ω

Calculate the current if the potential difference is increased to 120 V from 60 V with a current of 4 A from the source of a series circuit.

  1. 8 A

  2. 0.5 A

  3. 28,800 A

  4. 2 A

  5. 0.125 A

Show answer
Correct Option: A
Explanation:

V1 = 60 V, I1 = 4 A, R = V1/I1 = 60/4 = 15 ohms V2 = 120 V, R = 15 ohms I2 = V2/R = 120/15 = 8 A

If a device has a resistance of 10 Ω and current of 3 A, then calculate the heat developed in 20 s.

  1. 18 J

  2. 1800 J

  3. 0.005 J

  4. 0.5 J

  5. 4.5 J

Show answer
Correct Option: B
Explanation:

Electric current  = 3 A, Resistance  = 10 Ω, Time  = 20 s V = I x R = 3 x 10 = 30 V Heat produced = V x I x t = 30 x 3 x 20 = 1800 J

Which of the following properties of an alloy in a heating element used in a heater is true?

  1. An alloy does not consist of any metal

  2. Alloys decrease the tensile strength by adding a carbon agent.

  3. Alloys have very high resistance

  4. Alloy is designed to be able to operate at low temperatures.

  5. Alloys have a high melting point

Show answer
Correct Option: C
Explanation:

The heating element of the heater is made up of an alloy which has very high resistance so when current flows through the heating element, it becomes hot and glows red.

When we connect any devices in series with a battery in the ON position, what will happen?

  1. Current is constant

  2. Voltage is constant

  3. Current gets divided

  4. Current is equal to zero

  5. Voltage is zero

Show answer
Correct Option: A
Explanation:

A battery can be made to approximate a constant current source by adding a series resistance - the larger the resistance, the better the approximation - and the lower the current.

Why are coils of electric irons made of an alloy instead of using pure metal?

  1. Alloys oxidise quickly

  2. Alloys are mechanically weak

  3. Alloys better withstand less heat before melting

  4. Alloys have low resistivity than pure metal

  5. Alloys have a higher melting point

Show answer
Correct Option: E
Explanation:

Alloys have a higher melting point than pure metal. So, the coils of electric irons are made of an alloy.

Consider a conductor which passes 5 x 1016 electrons in 1 minute. Calculate the current flowing in the conductor.

  1. 0.133 mA

  2. 480 mA

  3. 7500 A

  4. 187.5 x 1035 A

  5. 0.0053 x 10-35 A

Show answer
Correct Option: A
Explanation:

The charge of an electron is = 1.6 x 10-19 coulomb i = n x e / t 5 x 1016 x 1.6 x 10-19 = 8 x 10-3. Therefore, charge passes across the section in one second, is 8 x 10-3 coulomb/60 second = 0.133 mA

If the resistance of a wire is 30 Ω with a length of 3 m and diameter of 0.4 mm, then calculate the resistivity of the wire.

  1. 11.25 x 10-6 Ωm

  2. 1.25 x 10-6 Ωm

  3. 80 x 106 Ωm

  4. 0.0125 x 10-6 Ωm

  5. 0.0013 x 10-6 Ωm

Show answer
Correct Option: B
Explanation:

R = 30 Ω, l = 3 m, diameter = 0.4 mm, radius = 0.2 mm = 0.2 x 10-3 m Area = πr2 = 3.14 x (0.2 x 10-3)2 = 0.125 x 10-6 m2 ρ = RA/l = 30 x 0.125 x 10-6/3 = 1.25 x 10-6 Ωm  

The potential difference applied to a device is 5 KV. Calculate the number of electrons per second where current through it is 3.2 mA.

  1. 5.12 × 10-21

  2. 0.19 × 1021

  3. 2 × 1016

  4. 16.38 × 10-25

  5. 0.061 × 1025

Show answer
Correct Option: C
Explanation:

Given: i = 3.2 x 10-3, t = 1, e = 1.6 x 10-19 i = q / t = ne / t n = it / e = 3.2 x 10-3 x 1 / 1.6 x 10-19 = 2 × 1016

If a device consumes energy 200 joules within a 4 second time period by providing a voltage of 120 V then calculate the power of the device.

  1. 50 Watts

  2. 800 Watts

  3. 0.02 Watts

  4. 2500 Watts

  5. 10000 Watts

Show answer
Correct Option: A
Explanation:

The power is simply the rate at which energy is supplied to a circuit or transformed by a circuit. In this case, the power is the energy consumed per time. P = (200 J) / (4 seconds) = 50 Watts

Calculate the resistance of each 4 resistors connected in parallel in the circuit, carrying a current of 5 A with voltage of 250 V?

  1. 50 ohm

  2. 200 ohm

  3. 312.5 ohm

  4. 0.08 ohm

  5. 0.02 ohm

Show answer
Correct Option: B
Explanation:

Resistance required in the circuit Rp = V/I = 250 V/ 5 A = 50 Number of resistors connected n = 4 Rp = r / n 50 = r / 4 Therefore, 50 x 4 = 200 ohm

If voltage is 110 V in a circuit, which consists of a power of 1300 W then calculate the resistance.

  1. 15730 K Ohms

  2. 0.084 Ohms

  3. 9.3 Ohms

  4. 143 K Ohms

  5. 11.81 Ohms

Show answer
Correct Option: C
Explanation:

R = V2 / P = (110)2 / (1300) = 9.3 Ohms

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