Two Mark Short Questions with Answer

ONE MARK QUESTIONS AND ANSWER

 

1. Define Electric current.

Electric current is defined as rate of flow of electric charge.

i = dq / dt amperes

where q is the charge in coulombs. The unit of current is the ampere which is the current that flows when 1 coulomb of charge is transferred in one second.

 

2. Define Electrical potential or Voltage.

This is generally measured between two points and its unit is volt. If the work done in moving a charge of one coulomb between any two points is 1 joule, then we say that the potential of one point with reference to the second point is 1 volt.

V = dW / dQ

where W is the work done in joules, Q is the charge in coulombs.

 

3. What is meant by resistance?

The resistance of a circuit is the property by which it opposes the flow of current. This parameter measured in Ohms is responsible for energy dissipation.

 

4. Define conductance.

The reciprocal of resistance is called conductance. Its unit is Siemen and its symbol is G.

G = 1/R

 

5. State Ohm's law (AU) Coimbatore/Mech - May 2003)

When the temperature remains constant, current flowing through a circuit is directly proportional to potential difference across the conductor.

Mathematically, we may write

V∞ I (Temperature being constant) (or) V = IR,

where 'R' the constant of proportionality, becomes the resistance where V is in volts and I is in amperes.

 

6. Define electrical power.

The rate at which work is, done in an electrical circuit is called electrical is power and its unit is joule per second or watt. When one coulomb of electric charge is be moved through a potential difference of one volt in one second, the rate of work is 938 one joule per second or one watt. Hence, power in electric circuits is obtained as a product of the voltage (E) and the current (I).

P = VI Watts

We may write this

P = I² R (or)

P = V² IR

 

7. What is meant by electrical energy? (AUCSE - May 2008)

Electrical energy is the total amount of work done and hence is the product of od dr power and time.

W = Pt = VIt = I² Rt = (V² / Rt ) joules (Watt-sec)

 

8. State Kirchhoff's laws.

Kirchhoff's Current Law (I Law)

The sum of the currents flowing towards a junction is equal to the sum of the currents flowing away from it.

Kirchhoff's Voltage Law (II Law)

In a closed circuit, the sum of the potential drops is equal to the sum of the potential rises.

 

9. Write the general form of mesh analysis.

 [R] [I] = [V]

 

10. Define Lumped circuits.

A network in which all the network elements are physically separable is known as lumped network. Most of the electrical networks are lumped networks.

 

11. Define linear and bilateral network.  (AUBCE - May 2007).

Linear Network

A circuit or network whose parameters i.e., elements like resistors, inductors and capacitors are always constant irrespective of the change in time, voltage, temperature etc., is known as linear network. In linear network, the Ohm's law can be applied and super position theorem can be used for solving mathematical equations.

Bilateral Network

A circuit whose characteristics, behaviour is same irrespective of the direction of current through various elements of it, is called bilateral network. Network consisting only resistors is a good example for bilateral network.

 

12. Define distributed elements. Given an example. (AU/BEE - Dec 2006)

A network in which the circuit elements like resistor, inductor, etc., cannot be physically separable for analysis purpose, is called distributed network.

For example, in a transmission line where resistance, inductance and capacitance are distributed all along its length. It cannot be shown as a separate element, anywhere in the circuit.

 

13. Define Non-linear network.

A circuit whose parameters change their values with change in time, temperature, voltage etc., is known as non linear network. Ohm's law and law of superposition do not applicable for this network.

 

14. Define Unilateral network.

A circuit whose operation, behaviour is dependent on the direction of the current through various elements is called unilateral network. Example for unilateral network is half wave diode rectifier.

 

15. Define active and passive network.

Active Network

A circuit which contains a source of energy is called active network. Voltage and current sources are energy sources.

Passive Network

A circuit which contains no energy source is called passive circuit. The passive network contains resistor, capacitor and inductor.

 

16. What are the types of circuit elements?

1. Active element:

Voltage and current sources

2. Passive element:

Resistor, inductor, capacitor

 

17. What are the dependent source? Name the different types? (AU/Coimbatore/EEE - May 2003)(AU/DIE, May 2001

Dependent sources

A dependent voltage or current source is one which depends on some other quantity in the circuit which may be either a voltage or a current. Such a source is represented by a diamond shaped symbol.

There are four types of dependent sources

1. Voltage dependent voltage source

2. Current dependent voltage source

3. Voltage dependent current source

4. Current dependent current source

 

18. Differentiate between time invariant and time variant sources. (AU/Coimbato re/EBBI May 2008);

Time invariant source

Source which can deliver or absorb energy continuously is called time invariant source.

Eg: Battery, DC generator, AC generator

Time variant source

Time variant source is one which depends on some other quantity in the circuit which may be either a voltage or a current.

Eg: Transistors, operational amplifier.

 

19. What is an ideal voltage source and an ideal current source?

Ideal Voltage Source

Ideal voltage source is a source which delivers energy with specified terminal voltage, which is independent of the current supplied by the source. Such a voltage which source maintains constant specified voltage for all currents supplied by the source is called an ideal voltage source. For ideal voltage source, the internal impedance is zero.

Ideal Current Source

The ideal current source is a source which delivers energy with a specified current which is independent of the voltage at its terminals. Such a current source which maintains a constant specified current for all voltages is called an ideal current source.

 

20. Draw the V-I relationship of an ideal voltage source.

 

21. What are the ideal sources of electrical energy?

1. Ideal voltage sources

2. Ideal current source

 

22. Draw the V-I relationship of an ideal current source.

 

23. Draw the V-I relationship of a practical voltage source.

 

24. Draw the V-I relationship of practical current source.

 

25. State Kirchhoff's current law.

Kirchhoff's Current Law (I Law)

Statement

The sum of the currents flowing towards a junction is equal to the sum of the currents flowing away from it.

In figure, A is a junction (or node) formed by six conductors. The currents in these conductors are 11, 12, ... I6. Some of these currents are flowing towards A and others flowing away from it.

According to Kirchhoff's Law,

I₁ + I₄  + I₅ + I₆ = I₂ + I₃

Current flowing towards A = Current flowing away from A

 

26. State Kirchhoff's voltage law

Kirchhoff's Voltage Law (II Law)

Statement

In a closed circuit, the sum of the potential drops is equal to the sum of the potential rises.

In figure, ABCDA form a closed circuit. Assuming the current direction as shown, from A to B, we have a potential drop of IR1 volts. Writing for the entire loop ABCDA, we have,

Sum of potential drops = IR₁+ IR₂ + IR₃

Potential rise from D to A = V

IR₁ + IR₂ + IR₃ = V

 

27. Write the current division rule.

 

28. What is the equivalent resistance when 'N' resistors are in (a) series (b) in parallel?  (AUECE - May 2007),

(a) Series Connection

(b) Parallel Connection

 

29. Mention the limitations of Ohm's law.  (AUCoimbatore . Mech)

1. Ohm's law does not apply to all non-metallic conductors.

2. It does not also apply to non-linear devices such as zener diode, vacuum tubes etc.

3. Ohm's law is true for metal conductors at constant temperature. If the temperature changes, the law is not applicable.

 

30. Compare series and parallel circuit.

 

31. What do you understand by Nodal analysis?

The nodal method is used to analyze multisource circuits. In this method that we solve the simultaneous equations using Kirchhoff's current law (KCL) applied at various nodes in an electric circuit. Node is defined as junction or joining point two or more component terminals.

 

32. Write the equivalent resistance when two resistors are connected in parallel.

R_eq = R₁ R₂ / R₁ + R₂

 

33. Give the expression for star to delta transformation.

 

34. All the resistors in delta are equal and converted into star network. Which network has the larger resistance?

Delta network has larger resistance

 

35. Give the expression for delta to star conversion.

 

36. Write the general form of nodal analysis.

[G][V]=[I]