Electricity

Question 1

Electric current

Answer 1

It is defined as the rate of flow of charges in a conductor.

I=Q/t

Question 2

SI unit of electric current

Answer 2

one ampere, when a charge of one coulomb flows across any cross-section of a conductor, in one second. Hence,

1 ampere = 1 coulomb / 1 second

Question 3

A charge of 12 coulomb flows through a bulb in 5 second. What is the current through the bulb?

Answer 3

Solution:

Charge Q = 12 C, Time t = 5 s. Therefore, current I = Q /t
12 /5 =I

2.4 A

Question 4

Used to fix the magnitude of the current through a circuit

Answer 4

Resistor

Question 5

Used to select the magnitude of the current through a circuit.

Answer 5

Variable resistor or Rheostat

Question 6

Used to detect the current and its direction

Answer 6

Galvanometer

Question 7

Used to provide protection to the electrical components. It also serves as a reference point to measure the electric potential.

Answer 7

Ground connection

Question 8

The electric potential

Answer 8

at a point is defined as the amount of work done in moving a unit positive charge from infinity to that point against the electric force.

Question 9

The electric potential difference

Answer 9

The electric potential difference between two points is defined as the amount of work done in moving a unit positive charge from one point to another point against the electric force.

V=W/Q

Question 10

The SI unit of electric potential or potential difference is

Answer 10

volt (V).

Question 11

1 volt

Answer 11

The potential difference between two points is one volt, if one joule of work is done in moving one coulomb of charge from one point to another against the electric force.

I volt = 1 joule / 1 coulomb

Question 12

Solved Problem-2

The work done in moving a charge of 10 C across two points in a circuit is 100 J. What is the potential difference between the points?

Answer 12

V=w/q
100/10
V=10

Question 13

A German physicist, who established the relation between the potential difference and current, which is known as Ohm’s Law.

Answer 13

Georg Simon Ohm

Question 14

Ohm’s law

Answer 14

Ohm’s law, at a constant temperature, the steady current ‘I’ flowing through a conductor is directly proportional to the potential difference ‘V’ between the two ends of the conductor.

I~v

Question 15

Resistance

Answer 15

Resistance of a material is its property to oppose the flow of charges and hence the passage of current through it. It is different for different materials.

From Ohm’s Law, v/i= R.

Question 16

The SI unit of resistance is

Answer 16

ohm
and it is represented by the symbol Ω

Question 17

Resistance of a conductor

Answer 17

is said to be one ohm if a current of one ampere flows through it when a potential difference of one volt is maintained across its ends

1 R= 1 volt / 1ampere

Question 18

Solved Problem-3

Calculate the resistance of a conductor through which a current of 2 A passes, when the potential difference between its ends is 30 V.

Answer 18

15 Ω

Question 19

the resistance of any conductor ‘R’ is directly proportional to the ______ and is inversely proportional to its_______

Answer 19

length of the conductor ‘L’
area of cross section ‘A’.

Question 20

the electrical resistivity of a material

Answer 20

the electrical resistivity of a material is defined as the resistance of a conductor of unit length and unit area of cross . Its unit is ohm metre.
¶ rho = RA/L

Question 21

of a conductor is a measure of the resisting power of a specified material to the passage of an electric current. It is a constant for a given material.

Answer 21

Electrical resistivity

Question 22

Nichrome is a conductor with highest resistivity equal to ______ Hence, it is used in making heating elements.

Answer 22

1.5 x 10^-⁶ Ωm.

Question 23

Conductance

Answer 23

Conductance

of a material is the property of a material to aid the flow of charges and hence, the passage of current in it.
G=1/R
defined as the reciprocal of its resistance

Question 24

Electrical conductivity of a conductor

Answer 24

Electrical conductivity of a conductor
is a measure of its ability to pass the current through it
σ=1/¶(rho)
The reciprocal of electrical resistivity of a material is called its electrical conductivity.

Question 25

Unit of conductance

Answer 25

ohm-¹.

Question 26

Unit of electrical conductivity

Answer 26

ohm-¹ metre-¹. Or mho meter-¹

Question 27

Resistivity of copper

Answer 27

1.62*10-⁸Ωm

Question 28

Resistivity of nickel

Answer 28

6.84*10-⁸ Ωm

Question 29

Resistivity of chromium

Answer 29

12.9*10-⁸

Question 30

Resistivity of glass

Answer 30

10¹⁰ to 10¹⁴

Question 31

Resistivity of rubber

Answer 31

10¹¹ to 10¹⁶

Question 32

The resistance of a wire of length 10 m is 2 ohm. If the area of cross section of the The wire is 2*10-⁷ m². determine its (i) resistivity call (ii) conductance and (iii) conductivity

Answer 32

¶ (rho)=RA/L Resistivity= 4*10-⁸Ωm Conductance G= 1/R 0.5 mho Conductivity (Sigma) 0.25*10⁸ mho m-¹

Question 33

The two basic methods of joining resistors together are:

Answer 33

a) Resistors connected in series, and b) Resistors connected in parallel.

Question 34

Series circuits are commonly used in devices such as

Answer 34

flashlights

Question 35

The equivalent resistance in a series combination is ______ than the highest of the individual resistances.

Answer 35

greater

Question 36

Three resistors of resistances 5 ohm, 3 ohm and 2 ohm are connected in series with 10 V battery. Calculate their effective resistance and the current flowing through the circuit.

Answer 36

effective resistance =10Ω Current=1A

Question 37

The equivalent resistance in a parallel combination is _____ the lowest of the ass individual resistances.

Answer 37

less than

Question 38

heating effect of current

Answer 38

the passage of electric current through a wire, results in the production of heat. This phenomenon is called heating effect of current H=I²Rt

Question 39

Joule's law of heating

Answer 39

. Joule's law of heating states that the heat produced in any resistor is: H=I²Rt directly proportional to the square of the current passing through the resistor. directly proportional to the resistance of the resistor directly proportional to the time for which the current is passing through the resistor.

Question 40

Nichrome, which is an alloy of Nickel and Chromium is used as the heating element. Why? Because:

Answer 40

(i) it has high resistivity, (ii) it has a high melting point, (iii) it is not easily oxidized.

Question 41

Application of heating effect

Answer 41

Electric heating device Fuse wire Filament in bulb

Question 42

Problem-6 An electric heater of resistance 5 2 is connected to an electric source. If a current of 6 A flows through the heater, then find the amount of heat produced in 5 minutes.

Answer 42

H=I²Rt, H=54000J

Question 43

power

Answer 43

is defined as the rate of doing work or rate of spending energy. Similarly, the electric power is defined as the rate of consumption of electrical energy

Question 44

Electric power

Answer 44

electric power is the product of s the electric current and the potential difference due to which the current passes in a circuit P=vi

Question 45

The SI unit of electric power

Answer 45

The SI unit of electric power is watt. When a current of 1 ampere passes across the ends of a conductor, which is at a potential difference of 1 volt, then the electric power is P= 1 volt x 1 ampere = 1 watt

Question 46

The horse power (hp)

Answer 46

The horse power (hp) is a unit in the foot-pound-second (fps) or English system, sometimes used to express the electric power. It is equal to 746 watt.

Question 47

Consumption of electricity is based on

Answer 47

Consumption of electricity is based on two factors: (i) Amount of electric power and (ii) Duration of usage.

Question 48

Electrical energy

Answer 48

Electrical energy consumed is taken as the product of electric power and time of usage

Question 49

Consumption of electrical energy is measured and expressed in watt hour, though its SI unit is

Answer 49

watt second

Question 50

One kilowatt hour is otherwise known as

Answer 50

one unit of electrical energy.

Question 51

One kilowatt hour means that an electric power of

Answer 51

1000 watt has been utilized for an hour.

Question 52

1watt second

Answer 52

3.6*10⁶ J

Question 53

is used to record the consumption of electrical energy

Answer 53

The meter

Question 54

The function of the L fuse wire or a MCB is to protect the house hold electrical appliances from

Answer 54

overloading due to excess current.

Question 55

An MCB is a switching device, which can be activated automatically as well as manually. It has a spring attached to the switch, which is attracted by an electromagnet when an excess current passes through the circuit. Hence,

Answer 55

the circuit is broken and the protection of the appliance is ensured

Question 56

One more advantage of the parallel connection of circuits is that each electric appliance gets an

Answer 56

equal voltage.

Question 57

The fuse wire or MCB will disconnect the circuit in the event of an

Answer 57

overloading and short circuiting.

Question 58

Over loading happens when a large number of appliances are connected in _______ to the same source of electric power. This leads to a flow of excess current in the electric circuit.

Answer 58

series

Question 59

overloading

Answer 59

When the amount of current passing through a wire exceeds the maximum permissible limit, the wires get heated to such an extent that a fire may be caused. This is known as Bat overloading.

Question 60

short circuit.

Answer 60

When a live wire comes in contact Wire with a neutral wire, it causes a 'short circuit. This happens when the insulation of the wires get damaged due to temperature changes or some external force. Due to a short circuit, the effective resistance in the circuit becomes very ever small, which leads to the flow of a large current through the wires

Question 61

With the help of the chemical compounds like ___________, the manufacturer can produce LED bulbs that radiates red, green, yellow and orange colours

Answer 61

Gallium Arsenide and Gallium Phosphide

Question 62

Merits of a LED bulb

Answer 62

1. As there is no filament, there is no loss of energy in the form of heat. It is cooler than the incandescent bulb. 2. In comparison with the fluorescent light, the LED bulbs have significantly low power requirement. 3. It is not harmful to the environment. 4. A wide range of colours is possible here. 5. It is cost-efficient and energy efficient. 6. Mercury and other toxic materials are not required

Question 63

The first LED television screen was developed by

Answer 63

James P. Mitchell in 1977

Question 64

______ introduced the first commercial LED Television.

Answer 64

2009, SONY

Question 65

Advantages of LED television

Answer 65

It has brighter picture quality. It is thinner in size. • It uses less power and consumes very less energy. Its life span is more. It is more reliable.

Question 66

Calculate the current and the resistance of a 100 W, 200 V electric bulb in an electric circuit

Answer 66

P=vi=I=p/v R=v/i 0.5 A 400 Ω

Question 67

Which of the following is correct? a) Rate of change of charge is electrical power. b) Rate of change of charge is current. c) Rate of change of energy is current. d) Rate of change of current is charge.

Answer 67

b) Rate of change of charge is current.

Question 68

Three resistors of 1 Ω, 2 2 and 4 2 are connected in parallel in a circuit. If a 1 Ω resistor draws a current of 1 A, find the current through the other two resistors

Answer 68

The potential difference across the 1 Ω resistor =I1*R1=1/1=1 V Since, the resistors are connected in parallel in the circuit, the same potential difference will exist across the other resistors also. So, the current in the 2 Ω resistor, V/R2=1/2=. 0.5A Similarly, the current in the 4 Ω resistor, V/R3=1/4=. 0.25A

Question 69

In a simple circuit, why does the bulb glow when you close the switch? a) The switch produces electricity. b) Closing the switch completes the circuit. c) Closing the switch breaks the circuit. d) The bulb is getting charged..

Answer 69

Closing the switch completes the circuit.

Question 70

Kilowatt hour is the unit of a) resistivity c) electrical energy b) conductivity d) electrical power

Answer 70

electrical energy

Question 71

Assertion: Electric appliances with a metallic body have three wire connections. Reason: Three pin connections in reduce heating of the connecting wires

Answer 71

if the assertion is true, but the reason is false.