Current Electricity MCQ Quiz - Objective Question with Answer for Current Electricity - Download Free PDF

The correct answer is Both electrons and holes.

Key Points

• Semiconductors are materials that have a conductivity between conductors (generally metals) and nonconductors or insulators (such as most ceramics).
• At room temperature, a semiconductor has enough free electrons to allow it to conduct current.
• At or close to absolute zero a semiconductor behaves like an insulator.
• The cause of electrical conduction in semiconductors is due to the movement of the holes in the valence band and the movement of the electrons in the conduction band.
• Conduction occurs at a higher temperatures because the electrons surrounding the semiconductor atoms can break away from their covalent bond and move freely about the lattice.
• Holes are formed when the electrons from the outermost shell of the atom that is completely filled with the electrons move out to the conduction band.
• When the electric field is applied then as a result the electrons will start moving in the conduction band in the direction opposite to that of the electric field.

The Correct Answer is Ampere (A).

Key Points

• Coulomb Per Second (C/s) is a unit in the category of Electric current.
• It is also known as coulombs per second, (coulomb/second).
• This unit is commonly used in the SI unit system.
• Coulomb Per Second (C/s) has a dimension of I where I is electric current.
• 1 coulomb of charge flows through any cross-section of a conductor in 1 second, the electric current through it is said to be 1 ampere.
• The SI unit of current is coulomb per second, generally known as ampere.

Additional Information

Second-

• The second (s or sec) is the International System of Units (SI) unit of time measurement.
• It is the time required for an electromagnetic (EM) field to propagate 299,792,458 meters (2.99792458 x 10⁸ m) through a vacuum.
• This figure is sometimes rounded to 3 x 10⁸ m, or 300,000 kilometers (3 x 10⁵ km).
• One second is equal to 1/86,400 of a mean solar day.
• This is easy to derive from the fact that there are 60 seconds in a minute, 60 minutes in an hour and 24 hours in a mean solar day.

Joule-

• It is equal to the amount of work done when a force of one newton displaces a mass through a distance of one metre in the direction of that force.
• It is also the energy dissipated as heat when an electric current of one ampere passes through a resistance of one ohm for one second.

Volt-

• Unit of electrical potential, potential difference and electromotive force in the metre–kilogram–second system (SI).
• It is equal to the difference in potential between two points in a conductor carrying one-ampere current when the power dissipated between the points is one watt.

The correct answer is Negative charge.

• A plastic scale after being rubbed against dry hair attracts bits of paper as it acquires a negative charge.
• The plastic scale gets electrically charged due to rubbing against dry hair.
• The plastic scale acquires charge due to static electricity.
• A temporary collection of charges will form near the rubbed surface of the plastic scale.
• The bits of paper are electrically neutral.
• Within the paper bits, the electrons get either attracted or repelled based on the charge of the plastic scale.
• The electrically charged scale exerts an electric force against the paper bits and attracts them.
• When a plastic scale is rubbed against dry hair, the material that has a stronger affinity for electrons pulls them from the other material.
  • A negative charge will produce on the material that has gained electrons.
  • A net positive charge will produce on the material that has lost electrons.

The Correct Answer is Silver.

Key Points

• The resistivity of Silver is 1.59×10⁻⁸ Ω⋅m.
• Silver is a chemical element with the atomic number 47 and the symbol Ag.
• It is a lustrous, soft, white transition metal with the highest electrical conductivity, thermal conductivity, and reflectivity of any metal.
• The metal can be found in its pure, elemental form in the Earth's crust, as an alloy with gold and other metals, and in minerals like argentite and chlorargyrite.
• The majority of silver is produced as a byproduct of the refining of copper, gold, lead, and zinc.

Important Points

• Electrical resistivity is a property that determines how well a material absorbs electric current.
• Electrical conductivity, its opposite, is a measurement of how well a substance conducts electricity. A material with a low resistivity allows electric current to pass through it easily. 
• The Greek letter ρ (rho) is used to represent resistivity.

Additional Information

The correct option is 1

Concept:

A cell is a device that produces an electrical current through a chemical reaction. When two or more cells are connected together, either in series or in parallel, they form a battery. The purpose of connecting multiple cells together is to increase the overall voltage (if in series) or the capacity/current (if in parallel) of the battery.

Let's look at the other options:

2. Electromagnet: This is a type of magnet in which the magnetic field is produced by an electric current. It's not related to the combination of cells.

3. Fuse: A fuse is a safety device used in electrical circuits. It's designed to break or melt when the current exceeds a specific value, thereby preventing excessive currents which could cause damage or fire.

4. Voltmeter: A voltmeter is an instrument used to measure the voltage (or electrical potential difference) between two points in an electrical circuit.

The correct answer is the Microwave.

Key Points

• A microwave oven uses microwaves to heat food.
• In the case of microwave ovens, the commonly used radio wave frequency is roughly 2,500 megahertz (2.5 gigahertz).
• Radio waves in this frequency range absorbed by water, fats, and sugars. When they are absorbed they are converted directly into atomic motion or vibration.
• Therefore heavy motion or vibration is converted into heat.

Important Points

• Microwaves are not absorbed by most plastics, glass, or ceramics.
• The frequency of the Microwave equals the resonance frequency of water. Therefore foods could be heated up by the oscillation of water molecules.

Additional Information

• An Electric heater, Electric blub (with filament), Electric iron is the electrical device that converts an electric current into heat.
• They working on the principle of the Joule heating effect.
  • An electric current passing through a resistor will convert that electrical energy into heat energy.

The correct answer is option 3)6000 ohm

Given:

\(V=12V,I=2mA=0.002A\)

To find:

Resistance (R)

Formula used:

Ohm's law: \(V=IR\)

Calculations:

As,

\(V=IR\)

\(R={V\over I}\)

\(R={12\over 0.002}=6000 ohm\)

Therefore, the value of Resistance is 6000ohm.

Key Points

• "Kirchhoff's Rules" belongs to electrical circuits.
• Kirchhoff’s loop rule explains that the sum of all the electric potential differences nearby a loop is 0.
• Sometimes, we also refer to it as Kirchhoff’s voltage law or Kirchhoff’s second law.
• In other words, it states that the energy in which the battery supplied get used up by all the other components in a loop.
• It is so because energy cannot enter or leave a closed circuit. 
• The rule is an application of the preservation of energy in terms of the electric potential difference.

CONCEPT:

• Some liquids are good conductors of electricity and some are poor conductors.
• Most liquids that conduct electricity are solutions of acids, bases and salts.
• The passage of an electric current through a conducting liquid causes chemical reactions. The resulting effects are called chemical effects of currents.

EXPLANATION:

These conduct electricity in their aqueous medium (dissolve in water).

• Vinegar is the common name of acetic acid and breaks into their ions in the aqueous medium.
• Lime juice is made of citric acid and it breaks into their ions in the aqueous medium.
• Saltwater is also broken into their ions in the aqueous medium.
• Distilled water is free of salts and is a poor conductor of electricity.

Hence, it becomes clear that Distilled water is not a conductor of electricity.

The correct answer is Rectifier.

Key Points

• A rectifier is a device that converts an oscillating two-directional alternating current (AC) into a single-directional direct current (DC).
• Rectifiers can take a wide variety of physical forms, from vacuum tube diodes and crystal radio receivers to modern silicon-based diode.
• There are two types of rectifiers: Half wave rectifier and full-wave rectifier.
  • Half-wave rectifiers work by eliminating one side of the AC, thereby only allowing one direction of current to pass through.
    • Since half of the AC power input goes unused, half-wave rectifiers produce a very inefficient conversion.
  • Full-wave rectifier eliminates AC from both the directions hence it is more efficient.
• Rectifier mostly used in Power supply, inverters etc.

Additional Information

Other devices and their functions:

The correct answer is Polyvinyl chloride.

Key Points

• Electric wires are generally coated with polyvinyl chloride.
• Electric wires are made up of materials like copper, that conduct electricity well.
• The electrical wires are made up of copper, so these wires cannot be laid bare inside the system.
• A coating of PVC is required to solely enhance the productiveness of the wires, it additionally presents safety to the person from getting an unconditional shock and it additionally points out to the consumer which wire is for which when the wires are coloured for distinct purposes. 
• This is because PVC is an insulator.

The correct answer is offer no resistance to the flow of current.

Key Points

• Superconductors are substances that have zero resistance at a very low temperature. so electricity flows through them rapidly.
• eg- Mercury below 4.2 K, Lead below 7.25 K acts like superconductors. (K= kelvin)

Additional Information

• Current flows in the opposite direction in which direction free electrons of a substance flow. This phenomenon is known as current electricity.
• A substance can be divided into four types based on the conductivity of the electricity or you can say based on the free electron number present on their surface:
  • Insulators: The substances that do not allow the current to flow through them. They don't have any free electrons.
    • eg- Cotton, Wood, Glass, etc.
  • Conductors: The substances that allow the current to flow through them are known as conductors. They have a large number of free electrons.
    • eg- Copper, Silver, Iron, Aluminium, etc.
  • Superconductors: This substance has zero resistance at a very low temperature. so electricity flows through them rapidly.
    • ​eg- Mercury below 4.2 K, and Lead below 7.25 K act like superconductors. (K= kelvin)
  • Semiconductors: Some substances that have electrical resistivity between those of conductors and insulators.
    • eg- Silicon and germanium.

The correct answer is Alloy of lead and tin.

Important Points

• Fuse is a protecting device used to save from the overcurrent in an electrical circuit.
  • The wire used in electric Instruments is made up of an alloy of lead and tin.
  • It will cuts off when a high current flows through the wire.
  • Fuse is connected in the live wire to avoid overloading.
  • It is characterized by high resistance and low melting point.
  • Electric fittings are earthed to prevent electric shock.

• Fuse resistance is a comparable thing, fuse has low resistance with comparison to the load resistance of the circuit but has high resistance when compared to the wire of the same length.
• Thus when asked whether a fuse has high resistance or low resistance, we should answer that a fuse has high resistance with a low melting point. 

Key Points

• Given: Current (I) = 1.5 A, Resistance (R) = 10 Ω, Time (t) = 1 minute = 60 seconds.
• Formula for energy dissipated: H = I²Rt, where H is heat energy in joules (J).
• Substituting: H = (1.5)² × 10 × 60 = 2.25 × 10 × 60 = 1350 J.
• Since 1 joule/second = 1 watt, total energy dissipated in 1 minute is 1350 J = 1350 W·s.
• Hence, energy dissipated is 1350 joules, which matches option 1 numerically (not unit-wise, see clarification below).

Additional Information

• Power (P)
  • P = I²R is the instantaneous power dissipated in a resistor.
  • Here, P = (1.5)² × 10 = 22.5 W (this is rate, not total energy).
• Energy (E) vs Power (P)
  • Energy = Power × Time.
  • Power is the rate at which energy is used; energy is the total work done or heat dissipated.
• Joule's Law of Heating:
  • Heat produced in resistor is proportional to square of current, resistance, and time (H = I²Rt).
• Unit Conversions:
  • 1 J = 1 W·s; 1 kWh = 3.6 × 10⁶ J.
  • In this question, energy is asked, so answer should be in joules, not watts.
• Correct Unit Clarification:
  • The numeric value 1350 is correct for energy in joules, but W (watt) is a unit of power, not energy.
  • The most precise answer should be 1350 J (Joules),

Tungsten metal is used for making the filament of electric bulbs.

Tungsten is used to making an electrical bulb filament for the following reasons:

• It's a very high melting point element.
• It has very high resistance, so it does not burn easily at room temperature.
• The lamp glows at high temperatures.
• Tungsten filament does not melt even though a significant amount of heat is generated due to the passing of the current through the filament (through the heating effect of the current).

Key Points

Tungsten has the highest melting point i.e.  3,410°C.

Argon is used in electric bulbs to prevent corrosion of its tungsten filament. Since it doesn't react with tungsten, it stops the filament from burning away in the presence of oxygen.

Hence, which results in increased light bulb life.

In the electric bulb, electric energy is converted into light energy.

Tungsten:

• Symbol: W
• Atomic number: 74
• Atomic mass: 183.84 u​ 

Additional Information