Electric Components MCQ Quiz - Objective Question with Answer for Electric Components - Download Free PDF

Explanation:

Unshielded Twisted Pair (UTP) Cables

Definition: Unshielded Twisted Pair (UTP) cables are a type of twisted pair cables that are commonly used for various telecommunications and networking applications. They consist of pairs of wires twisted together to reduce electromagnetic interference (EMI) from external sources and crosstalk between adjacent pairs within the cable.

Working Principle: UTP cables work by twisting the pairs of wires together, which helps to cancel out electromagnetic interference (EMI) from external sources and minimize crosstalk between the pairs. The twisting of the wires causes the magnetic fields generated by the current in each wire to cancel each other out, thus reducing the overall EMI.

Advantages:

• Cost-effective: UTP cables are generally less expensive than shielded cables, making them a popular choice for many networking applications.
• Ease of installation: UTP cables are lighter and more flexible, making them easier to install and handle compared to shielded cables.
• Widely used: UTP cables are commonly used in local area networks (LANs) and other telecommunications applications.

Disadvantages:

• Susceptibility to EMI: UTP cables do not have shielding, which makes them more susceptible to electromagnetic interference (EMI) compared to shielded cables.
• Limited distance: UTP cables are typically used for short-distance communication due to their susceptibility to EMI and signal attenuation over longer distances.

Applications: UTP cables are widely used in various applications, including local area networks (LANs), telephone systems, and other telecommunications infrastructure where cost and ease of installation are important considerations.

Correct Option Analysis:

The correct option is:

Option 1: They have a higher resistance to EMI than STP cables.

This option is incorrect because UTP cables do not have shielding, which makes them more susceptible to electromagnetic interference (EMI) compared to Shielded Twisted Pair (STP) cables. STP cables have a layer of shielding that provides additional protection against EMI, making them more resistant to interference than UTP cables. Therefore, it is not true that UTP cables have a higher resistance to EMI than STP cables.

Important Information

To further understand the analysis, let’s evaluate the other options:

Option 2: They are commonly used in local area networks (LANs).

This option is true. UTP cables are indeed commonly used in local area networks (LANs) due to their cost-effectiveness, ease of installation, and adequate performance for short-distance communication needs.

Option 3: They are lighter and more flexible than STP cables.

This option is also true. UTP cables are lighter and more flexible than STP cables because they do not have the additional shielding layer present in STP cables. This makes UTP cables easier to handle and install.

Option 4: They are cost-effective for short-distance communication.

This option is true as well. UTP cables are cost-effective for short-distance communication because they are less expensive to produce and install compared to shielded cables. Their performance is sufficient for many short-distance networking applications, making them a popular choice.

Conclusion:

Understanding the characteristics of UTP and STP cables is essential for choosing the right type of cable for specific applications. UTP cables, while cost-effective and easy to install, are more susceptible to EMI compared to STP cables due to the lack of shielding. This makes them suitable for short-distance communication in environments with minimal EMI, such as local area networks (LANs). On the other hand, STP cables provide better protection against EMI and are preferable in environments with higher levels of electromagnetic interference.

The correct answer is: 2) Lower cost and easier installation

Explanation:

Unshielded Twisted Pair (UTP) cables have the following advantages over Shielded Twisted Pair (STP):

1. Lower Cost: UTP cables do not require shielding materials (e.g., foil, braided mesh), making them cheaper to manufacture.

2. Easier Installation: UTP cables are lighter and more flexible due to the absence of shielding, simplifying routing and termination.

Why Not the Other Options?

1.  Better performance in industrial environments → STP is superior in high-EMI (electromagnetic interference) areas like factories.

2.  Complete resistance to EMI → UTP has no shielding, so it is more susceptible to EMI than STP.

3.  Higher durability → Shielding in STP can provide extra mechanical protection, making it more durable in harsh conditions.

Concept:

• The total number of protons and neutrons in the nucleus of an atom is known as its Mass Number and is denoted by A.
• Protons and neutrons are situated in the nucleus of an atom and contribute most to the mass of the elements as the mass of electrons is negligible.
• The atomic number of an atom is the same as a number of proton.

Additional Information

Mass number(A) = Number of protons (Z) + Number of neutrons (N)

It is represented by:

​

Mistake PointsIt is conventional to count the number of protons as atomic numbers and not the number of the neutron.

The number of neutrons can be changed and as so nuclear bombs are made. so we count only the number of protons and not neutrons.

Concept:

• Lenz’s law: When a voltage is generated by a change in magnetic flux.
• According to Faraday's law, the polarity of the induced voltage in an inductor is such that it produces a current whose magnetic field opposes the change which produces it.
• For example, if the current through an inductor is increasing, the induced voltage will be positive at the terminal through which the current enters, tending to oppose the additional increase in current.

• The magnitude of the induced emf is given by Faraday's Laws of Electromagnetic Induction. 
• Faraday's Laws of Electromagnetic Induction: Whenever the number of magnetic lines of force (magnetic flux) passing through a circuit changes an emf is produced in the circuit called induced emf. The induced emf persists only as long as there is a change of flux.

The induced emf is given by the rate of change of magnetic flux linked with the circuit i.e.

\(e=-\frac{d\text{ }\!\!\Phi\!\!\text{ }}{dt}\)

Where dΦ = change in magnetic flux and e = induced e.m.f

CONCEPT:

• Ohm’s law: At constant temperature, the potential difference across a current-carrying wire is directly proportional to the current flowing through it.

          i.e. V = IR

Where V = potential difference, R = resistance and I = current.

CALCULATION:

Given V = 18 V and R = 3 Ω,

• According to ohm's law:

⇒ ​V = IR

⇒ I = V/R

⇒ I = 18/3 = 6 A

• The sensation of electric shock is caused by the flow of electric current through the human body to the earth.
• When a person comes in contact with electrically live objects like water heaters, washing machines electric iron, etc., the extent of damages caused by this current depends on its magnitude and duration.
• This kind of current is called the leakage current which comes in milli-amps.
• These leakage currents being very small in magnitude, hence undetected by the fuses/MCBs are the major cause for the fires due to electricity.
• Residual current operated circuit breakers provide maximum protection from electric shocks and fires caused due to earth leakage current and also prevents the waste of electrical energy.
• These residual current circuit breakers (RCCB) are popularly called as earth leakage circuit breakers (ELCB).

Concept:

The resistance of copper wire is given by:

\(R = \rho \frac{l}{A}\)

ρ = Resistivity of the wire

l = length of the wire

A = Area of the cross-section of the wire

Calculation:

Given Resistance of copper wire is 'R'

For a constant cross-sectional area, the resistance is directly proportional to length, i.e.

R ∝ l

If the length is doubled, the resistance will also be doubled. 

So the resistance of the new wire is:

R' = 2R

Four such wires connected in parallel is as shown:

The equivalent resistance is therefore R/2

 SI units:

• Conductivity is the reciprocal of resistivity.
• The resistance offered by a wire of unit length and unit area of cross-section is called resistivity or specific resistance (r).
• Resistance is the ratio of applied potential difference (V) to the current (I) flowing through the conductor.
• Conductance is the reciprocal of resistance.

• The curve for Ohm's Law in an ohmic conductor follows a straight line.
• This can be inferred from the definition for Ohms's Law which states that the potential difference (voltage) across an ideal conductor is proportional to the current through it, i.e.

          (V ∝ I).

• As the relation between the two quantities if of direct proportionality graph will be linear.

Fuse:

• A fuse is an electrical safety device that operates to provide overcurrent protection of an electrical circuit. 
• Fuses are widely used for the protection of electric motor circuits against small overloads and short circuits.
• The motor protection circuit will open the controlling contactor automatically, and the fuse will only operate for short-circuits or extreme overload.

Resistance:

The property of any conductor that opposes the flow of electric current through it is called resistance.

Mica

1. Mica is a naturally occurring non-metallic mineral that is based on a collection of silicates. 

2. Mica is used extensively in the electrical and electronic industry because of its dielectric strength and insulating properties.

Semiconductor:

Semiconductors are those elements that conductivity lies between conductor and insulator.

The capacity of a battery is measured in ampere-hours.

The ampere-hour capacity is equal to the product of the current in amperes and the time in hours during which the battery is supplying current.

The ampere-hour capacity varies inversely with the discharge current. The size of a cell is determined generally by its ampere-hour capacity.

The capacity of a cell depends upon the following factors:

• The area of the plates in contact with the electrolyte
• The quantity and the specific gravity of the electrolyte
• The type of separators
• The general condition of the battery (degree of sulfating, plates buckled, separators warped, sediment in the bottom of cells, etc)
• The final limiting voltage

A nickel-cadmium battery (NiCd or NiCad) is a rechargeable battery used for portable computers, drills, camcorders and other small battery-operated devices requiring an even power discharge.

NiCd batteries use electrodes made of nickel oxide hydroxide, metallic cadmium and an alkaline electrolyte of potassium hydroxide and deionized water.

Reactions:

The chemical reactions at the cadmium electrode during discharge are:

Cd + 2OH^- → Cd(OH)₂ + 2e^-

The reactions at the nickel oxide electrode are:

2NiO(OH) + 2H₂O + 2e^- → 2Ni(OH)₂ + 2OH^-

The net reaction during discharge is

2NiO(OH) + Cd + 2H₂O → 2Ni(OH)₂ + Cd(OH)₂

Advantages:

• Good performance in high-discharge and low-temperature applications
• Long shelf and use life

Disadvantages:

• Cost is more than the lead-acid battery
• These batteries have lower power densities

Concept:

The resistance of the conductor is given by:

\(R = \frac{{\rho l}}{A}\)

Where ρ = resistivity of the material

l = length of conductor

A = area of cross-section

Calculation:

For the second conductor:

\(R' = \frac{{\rho 2l}}{{A'}}\)

Given R’ = R

\(\frac{{\rho l}}{A} = \frac{{\rho 2l}}{{A'}}\)

A chopper is a static device that is used to obtain a variable dc voltage from a constant dc voltage source. Also known as a dc-to-dc converter.

Types of Choppers:

• Type A Chopper or First-Quadrant Chopper
• Type B Chopper or Second-Quadrant Chopper
• Type C Chopper or Two-quadrant type-A Chopper
• Type D Chopper or Two-quadrant type-B Chopper
• Type E Chopper or fourth-quadrant Chopper

The circuit diagram of Type B Chopper is as shown:

• When the chopper is ON, 'E' voltage drives a current through L in a direction opposite to that shown in the figure.
• During the ON period of the chopper, the inductance L stores energy.
• When Chopper is OFF, diode D conducts, and part of the energy stored in inductor L is returned to the supply.
• Therefore the average output voltage is positive and the average output current is negative as shown:

• In this chopper, power flows from load to source.
• Class B chopper is used for regenerative braking of dc motor.
• Class B chopper is a step-up chopper.

• HRC Fuse or High Rupturing Capacity Fuse.
• In that type of fuse, the fuse wire or element can carry short circuit heavy current for a known time period.
• During this time if the fault is removed, then it does not blow off otherwise it blows off or melts.