Basic Electrical

Resistance in Series/Parallel Connection

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Resistance in Series:-

More than one resistances can be connected either in series or in parallel connections. Now if we connect two resistances end on end then they are said to be connected in series.  Let’s take an example: Consider three resistances R1 and R2 be connected in series as shown below:

Series Connection

Now Equivalent resistance of this circuit equals to the sum of individual resistances,let’s prove it now:
In series circuit
(1) Same current flows through each resistance.
(2) Voltage drop across each resistance is different.
(3) Net voltage drop applied across circuit equals the sum of all voltage drops across each resistance

Therefore Vs= V1 + V2 = IR1 + IR2

Since Vs= IR 
(R is the equivalent resistance of circuit)

Then      IR = IR1 + IR2
              IR = I (R1+R2)
Cancelling out I from both sides we get

                  R = R1 + R2

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Series & Parallel connections of resistor

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Resistances in Parallel:-

As shown In below figure Resistances are said to be connected in Parallel connection.

In parallel circuit 
(1) Potential difference across all resistances is same.
(2) Current flowing through each resistance is different.
(3) Net current flowing through circuit is sum of three currents.


             I = t1 + t2 + t3  = V/r1 + V/r2 + V/r3

             Also I = V/R
where V is the voltage applied and R is the equivalent resistance of circuit

              So V/R =  V/r1 + V/r2 + V/r3

                    1/R = 1/r1 + 1/r2 + 1/r3

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Transformer MCQ

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Electrical Energy

Basic Electrical / By

What is Electric Energy? Definition & Example

Definition

Electric Energy is the product of Electric Power taken by the device and the time period.

Equation

Electric Energy = Electric Power(Watt) * Time(Hour)

Units

It is measured in Watt-Hour. As Electric Power is measured in Watt and Time is measured in Hour, So Product of Power(Watt) and Time(Hour) is Watt-Hour.

1 Watt-Hour equals to 1 Watt of Power released for 1 Hour. In terms of Joules 1 Watt-Hour equals to 3600 Joules (3.6*10³ Joules) of Energy. Mostly Joule is used as unit of Energy Except Electrical Energy.


Used to Measure Electricity Bill 

Since In Asia Electricity Bill is generated by computing No. of Units consumed by the consumer, then multiplying the same with the tariff or rate of one Unit. Unit is calculated with the help of Electric Energy Meter installed at the premises of Consumer.

Let’s take an Example

Consider A consumer consumes 100 Units of Energy. The tariff rate at their area is 5 rupees per unit. What is their Electricity Bill?

Solution : Here No. of Units = 100

                 Rate of one Unit   = 5

                 Electricity Bill = 100*5 = 500 rupees Answer

Now the Question rises How much one Unit Equals to?

So The answer is One Unit equals to 1 KWH  which is unit of Electric Energy, 

One KWH equals to 1 KW of Power drawn by the device during one hour.

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Example

If A 100 W Bulb glows for 10 Hours then How much Units does it Consume?

Solution: Here Power = 100 W

                         Time  = 10 H

So Electrical Energy  = 100*10 = 1000 W-H

1000W-H = 1 KWH = 1 Unit

So If A 100 W Bulb glows or 10 Hours then it consumes 1 Unit, Similarly if it glows for 20 Hours then it consumes 2 Unit.

In a similar fashion we can Calculate Units consumed by different devices used at home and then calculate our Electricity Bill. 

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power system mcq

Electric Power

Basic Electrical / By

Electric power is basically amount of Electric Energy used in a particular span of time. It is measured in watts.

Electric Power (watts) = Electrical Energy (Joule)/Time (Second)

Ø  If a device consume 1 Joule of energy in one second then power is 1 Watt.

As Power = 1 (joule)/1 (second) =1 Watt

So it’s clear Power is measure of energy per unit time like a second, it’s better to say Watt rather than joule/second.

Another definition:

Electric Power is product of Voltage (V) supplied to a device and Current(A) drawn by the device.

Electric Power (watts) = Voltage * Current

P = V*I

Let’s take an Example:-

·         Consider a Motor is feed with 220V supply and it draws 10A of load then what is Power of Motor?

Solution: Here Voltage (V) = 220V

                            Current (I) = 10A

                So Power = V*I

                                   = 220*10   = 2200 Watt

Since 1 KW = 1000W

Then 2200 Watt = 2200/1000 = 2.2KW

So Motor Power= 2.2KW Answer

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Basic Electrical MCQ

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Previous
Next

1. An electric current is the

  1. storage of charge
  2. flow of electrons
  3. ionization of atom
  4. opposition to electrons

Answer: 2

2. The dielectric material used in variable capacitor is generally

  1. air
  2. mica
  3. ceramic
  4. electrolyte

Answer: 1

3. How many electrons will constitute 2 Coulombs of charge?

  1. 6.24 * 1018 electrons
  2. 12.48 * 1018 electrons
  3. 1.602 * 1019 electrons
  4. 3.204 * 1019 electrons

Answer: 2
Explanation: One Coulomb of charge consists of 1/(1.602*10-19) electron that is 6.24 * 1018 electrons. A coulomb is a unit for the charge. Thus, for 2 Coulombs of charge will have 6.24 * 1018 * 2 = 12.48 * 1018 electrons.

4. What is responsible for the current to flow?

  1. Protons
  2. Electrons
  3. Nucleus
  4. Protons and Electrons

Answer: 2
Explanation: For the current to flow in a circuit electrons are required. Electrons are negatively charged and when the potential difference is applied these electrons flow to constitute a current. The current direction is opposite to the electron flow.

5. Which of the following type of circuits in electrical engineering cannot be analyzed using Ohm’s law?

  1. Unilateral
  2. Bilateral
  3. Linear
  4. Conductors

Answer: 1
Explanation: Ohm’s law cannot be used for analyzing unilateral networks as such networks only allow current flow in one direction. A unilateral network can consist diode, transistor, etc.

6. Which of the following is correct about direct current?

  1. Frequency is zero
  2. Can be transported to larger distances with less loss in power
  3. Flows in one direction
  4. Magnitude is constan

Answer: 1
Explanation: A direct current has a fixed value and does not change with time. The frequency of the direct current is equal to zero as it does not change with time.

7. A capacitor consists of two

  1. insulation separated by a dielectric
  2. ceramic plates and one mica disc
  3. silver-coated insulators
  4. conductors separated by an insulator

Answer: 4

8. In a cable capacitor, voltage gradient is maximum at the surface       of the

  1. sheath
  2. earth
  3. conductor
  4. insulator

Answer: 3

9. The capacitance of a cable capacitor depends on

  1. core diameter
  2. ratio of cylinder radii
  3. potential difference
  4. insulation thickness

Answer: 2

10. The time constant of an R-C circuit is defined as the time during     which capacitor charging current becomes ——— percent of its        —— value.

  1. 37, initial
  2. 37, final
  3. 63, initial
  4. 63, final

Answer: 1

Basic Electrical MCQ

Basic Electrical / By
Next

1. With the rise in temperature the resistance of carbon

  1. decreases
  2. increases
  3. remain constant
  4. none of the above

Answer: 1

2. When number of capacitors are connected in series, then the equivalent capacitance is

  1. increases
  2. decreases
  3. remain same
  4. none of the above

Answer: 2

3. Which of the following elements of electrical engineering cannot be analyzed using Ohm’s law?

  1. Capacitors
  2. Inductors
  3. Transistors
  4. Resistance

Answer: 3
Explanation: Ohm’s law cannot be used for unilateral networks as such networks only allow current flow in one direction. Transistor forms a unilateral network. Thus, Ohm’s law cannot be used on Transistors.

4. According to the fundamentals of electrical engineering, which of these is a correct representation of peak value in an AC Circuit?

  1. RMS value/Peak factor
  2. RMS value*Form factor
  3. RMS value/Form factor
  4. RMS value*Peak factor

Answer: 4
Explanation: A peak factor in an AC circuit represents the ratio of the peak value to the RMS value. The peak factor also called the crest factor indicates how extreme the peaks are present in a waveform.

5. How many cycles will an AC signal make in 2 seconds if its frequency is 100 Hz?

  1. 200
  2. 150
  3. 100
  4. 50

Answer: 1
Explanation: In electrical engineering, the frequency represents the ratio of the number of cycles to the total time. Since frequency is given as 100 Hz and the time is 2 sec thus a total of 200 cycles will be made.

6. Which of the following is correct about the power consumed by R1 and R2 connected in series if the value of R1 is greater than R2?

  1. R1 will consume more power
  2. R2 will consume more power
  3. R1 and R2 will consume the same power
  4. The relationship between the power consumed cannot be established

Answer: 1
Explanation: In the introduction to electrical engineering it is explained that the power can be expressed as P = I2*R. When two resistors are connected in series the current flowing through the resistors is the same and thus, power consumed by the larger resistor will be more.

7. What kind of quantity is an Electric potential?

  1. Dimensionless quantity
  2. Tensor quantity
  3. Vector quantity
  4. Scalar quantity

Answer: 4
Explanation: Electric potential refers to the work done to bring a unit positive charge from a point with higher potential to a point with lower potential. Since electric potential only has magnitude but no direction, it is a scalar quantity.

8. Who defined electric current and devised a method to measure current?

  1. Andre-Marie Ampere
  2. Nikola Tesla
  3. Alessandro Antonio Volta
  4. Michael Faraday

Answer: 1
Explanation: Andre-Marie Ampere is a French physicist and mathematician who defined electric current and devised a method to measure current in the 1820s.

9. An inductor is a device which store energy in the form of

  1. magnetic field
  2. electric field.
  3. both electric and magnetic field.
  4. voltage and current.

Answer: 1

10. A capacitor is a device designed to store energy in the

  1. magnetic field
  2. electric field.
  3. both electric and magnetic field.
  4. plates

Answer: 2