Important Questions (1 Mark): Electricity - UPSC MCQ

Time rate of work done or electric energy develop or consumed by generator or appliance, is called electric power. We know, that the rate of work done per unit Time is known as power. So, here is some change ie., in terms of electricity Time rate of work done is known as electric power. 

Firstly, you get shorter battery life simply because your average energy consumption is increased over the peak period.A battery generates power when it powers a light bulb. It dissipates power when it is being charged.

Power is directly proportional to the potential difference and potential difference is directly proportional to the Current. In a series combination, Resistance is increased and thus the flow of current decreases Power is directly proportional to current therefore power decreases.

As more and more resistors are added in parallel to a circuit, the equivalent resistance of the circuit decreases and the total current of the circuit increases.Therefore the power decreases.

Power  =  voltage * current
Here, power = 100 W, voltage = 200 V 
P  = V*I 
Therefore, 100  = 200  * I 
I   = 100/200 A
I   =  0.5 A

Energy is the ability to do work, where work is done when a force moves an object. We need and we use energy every day, and energy is available in all different forms. Electrical energy is energy that is stored in charged particles within an electric field. 

Joule is the unit of work or energy; it is equal to the work done by a force of one newton acting through one meter. It was named in honor of the English physicist James Prescott Joule. It equals 107 ergs, or approximately 0.7377 foot-pounds. In electrical terms, the joule equals one watt-second—i.e., the energy released in one second by a current of one ampere through a resistance of one ohm.

To convert kilowatt-hours (kWh) to joules, it is essential to understand the relationship between these units of energy.

• 1 kilowatt (kW) equals 1,000 watts.
• 1 hour is equal to 3,600 seconds.
• To find joules in a kilowatt-hour, use the formula:
• Energy (in joules) = Power (in watts) × Time (in seconds)
• Thus, 1 kWh can be calculated as:

1 kWh = 1,000 watts × 3,600 seconds

When you multiply these values, you get:

• 1 kWh = 3,600,000 joules
• This can also be expressed in scientific notation as: 3.6 × 10⁶ joules.

When electric current flows through a conductor, it generates heat.

• As the current passes through, the conductor's resistance converts some of the electrical energy into heat.
• This process is known as Joule heating, which occurs in all conductive materials.
• The amount of heat produced depends on:
• The strength of the current.
• The resistance of the conductor.
• The duration of the current flow.
• In many applications, this heat is beneficial (e.g., in electric heaters) or undesirable (e.g., in electronic devices where overheating can be harmful).

When electric current flows through a conductor:

• Free electrons move within the conductor.

• Atoms in the conductor remain relatively stable and do not move.

• Atoms do not attract or repel free electrons significantly during the flow of current.

• This movement of free electrons creates a flow of electric charge, which constitutes the electric current.

When electrons starts drifting into lower potential to higher potential then it get collision with their atoms. Due to which electron loses their kinetic energy and cause heat effect of current.

Insulating materials are substances that inhibit the flow of electricity, heat, or sound. They are essential in various applications, such as electrical wiring and thermal insulation.

When identifying insulating materials, consider the following:

• Conductors: Materials like copper, gold, and silver are excellent conductors of electricity. They allow electric current to flow easily.
• Insulators: These materials resist the flow of electricity. A common example of an insulating material is paper, which is often used in electrical insulation.

In summary, paper is an insulating material, while copper, gold, and silver are all conductors.

Energy = v × i × t = 6 × 0.5 × 20 = 60J

Nichrome is the preferred material for heating elements in electric heating appliances due to its excellent properties. Here are the main reasons why nichrome is commonly used:

• High resistance: Nichrome has a high electrical resistance, which allows it to generate heat efficiently when an electric current passes through it.
• Durability: It can withstand high temperatures without degrading, making it suitable for prolonged use.
• Corrosion resistance: Nichrome is resistant to oxidation and corrosion, ensuring a longer lifespan compared to other metals.
• Stable performance: It maintains consistent heating performance even under varying conditions.

While other metals like brass, silver, and copper have their uses, they do not provide the same combination of durability and efficiency as nichrome in heating applications.

In domestic electric circuits, the cheapest appliance used is fuse bulb . 
An electric fuse is used as a safety device for the protection of electric circuits and appliances due to short - Circuiting or overloading of the electric circuits. 

20 Divisions are equal to the 2A
1 division is equal to 2/20 = 0.1 A
therefore Least count of the Ammeter is 0.1 A.

Least count L. C = 0.5 / No. of divisions 
Least count of voltmeter L. C = 0.5/20
 => 0.025 

We know that the voltmeter is always connected in parallel across the resistance to measure voltage across the resistance. So, option ( b) is the correct answer.

Resistance ‘R = 6ohm’ is related to length ‘L’, area of cross-section ‘A’ and resistivity ‘ρ’ as,

R = ρL/A

When L is doubled ,

As we know that the volume of the wire remains same.

old volume = new volume

AL = A'L' ....(i) ( as volume = area x length )

L' = 2L

So, from (i)

A' = A/2

So the new resistance is ,

R' = ρL'/A'

or

R' = ρ(2L)/(A/2) = 4 (ρL/A)

=> R' = 4R

thus, correct answer is option (b).

Electric pressure is also called as voltage or electrical potential. 1 volt is the amount of pressure required to flow one ampere of electricity through one ohm of resistance.
The difference in the electric potential between the two points is known as voltage. 

Substances with no free electrons are known as insulators. These materials do not allow electric current to flow through them easily. Here are some key points about insulators:

• Insulators have tightly bound electrons, preventing them from conducting electricity.
• Common examples include rubber, glass, and plastic.
• They are essential in electrical applications to protect against accidental shocks.
• Insulators can also reduce energy loss in electrical systems.

In contrast, other types of materials include:

• Electrolytes: These substances conduct electricity when dissolved in water.
• Conductors: Materials, like metals, which allow electricity to flow easily.
• Semiconductors: These materials have properties between conductors and insulators and can conduct electricity under certain conditions.

Substances with few free electrons are classified based on their electrical properties.

• Conductors: Materials that allow easy flow of electricity due to a high number of free electrons.
• Insulators: Substances that resist electrical flow, characterised by very few free electrons.
• Semiconductors: Materials that have properties between conductors and insulators, often used in electronic devices.
• Electrolytes: Solutions that conduct electricity when dissolved in water, typically composed of ions.

In summary, substances with a limited number of free electrons are best described as insulators. These materials do not facilitate electrical flow effectively.

Electrically neutral atoms simply possess the same number of electrons as protons. This gives the object a balance of both type of charge.

A body becomes positively charged when it loses certain particles.

• When a body loses electrons, which have a negative charge, it results in a net positive charge.
• Electrons are much lighter than protons and neutrons, making them the primary carriers of electric charge.
• In contrast, losing protons would actually make a body negatively charged, as protons are positively charged.
• Neutrons are neutral particles; their loss does not affect the overall charge of the body.
• α-particles consist of two protons and two neutrons. Losing these would also impact the charge, but it is not the primary mechanism for a body to become positively charged.

The process of losing electrons, therefore, is the key mechanism through which a body gains a positive charge.

Electrons have negative energy. When the number of electrons and protons are equal the charge is neutral but if electron is added to it then the negative charge dominates which gives it negative charge.