Lecture#06 Capacitor and Inductor

Instructor: M. Mateen Yaqoob

Quiz # 2 (1/3)

Q 1: How will you define 1 Watt (W) of Power?Q 2: What is the significance of kilowatt-hour (kWh)?Q 3: Calculate total cumulative power consumption (kWh) of following:• 1 device using energy of 120J for 5 sec and total running time is 2hours• 2 devices consuming 300W for 12 hours• 4 devices using 250W for 8 hours

Q 4: A battery has potential difference of 20 Volts is connected to 2KΩ resistor. Calculate power dissipation across the resistor?Q 5: What is the difference between resistor power rating and Ampere-hour rating. Elaborate each with the help of example

Quiz # 2 (2/3)

Q 6: If you vary the rheostat in the circuit shown in figure, you can change the amount of current. The setting of rheostat is such that current is 250mA.

1. What is the value of resistance in this configuration?

2. If the desired current is changed to 1A then what is new value of resistance?

Q 7: A power supply has potential difference of 12Volts and it is connected to a resistor of 10kΩ. Battery is operating for 24hours. Determine;

1. Ampere-hour rating2. What will be effect on operating

time of battery if it is required to operate on 2mA

3. Operating time of battery if ampere-hour rating is 80Ah at 2.5A

Quiz # 2 (3/3)

Q 8: Determine which resistor is been damaged by overheating and which is not

20mA

0.520

2

1/8

1mA

3k

Introduction

• Resistor: a passive element which dissipates energy only• Two important passive linear circuit elements:

1) Capacitor2) Inductor

• Capacitor and inductor can store energy only and they can neither generate nor dissipate energy.

Capacitors

• A capacitor consists of two conducting plates separated by an insulator (or dielectric).

(F/m)10854.8

ε

120

0

r

d

AC

When a voltage source v is connected to the capacitor, the source deposits a positive charge q on one plate and a negative charge −q on the other. The capacitor is said to store the electric charge.

Capacitance The amount of charge that a capacitor can store per unit of voltage across its plates is its capacitance, designated C. That is, capacitance is a measure of a capacitor's ability to store charge. The more charge per unit of voltage that a capacitor can store, the greater its capacitance, as expressed by the following formula:

By rearranging the terms C=Q/V, we can obtain two other formulas. Q= CV V= Q /C

The Unit of Capacitance The farad (F) is the basic unit of capacitance. Recall that the coulomb (C) is the unit of electrical charge.

One farad is the amount of capacitance when one coulomb (C) of charge is stored with one volt across the plates.

Although the capacitance C of a capacitor is the ratio of the charge per plate to the applied voltage v, it does not depend on q or v.

Three factors affecting the value of capacitance:

1. Area: the larger the area, the greater the capacitance.2. Spacing between the plates: the smaller the spacing,

the greater the capacitance.3. Material permittivity: the higher the permittivity, the

greater the capacitance.

dA

Cε