KEY NOTES
Subject: Physics Chapter: 12- Electricity
1. If a net charge Q, flows across any cross-section of a conductor in time t, then the
current I, through the cross-section is ________
2. Electric current is the rate of flow of __________
3. 1ampere = 1____________ / 1_______
4. The charge of an electron is______________
5. The electrons move only if there is a difference of electric pressure – called the
___________ _____________
6. A voltmeter is connected in ________________ and an ammeter in _______________.
7. The ammeter reading ___________ with change in position in the electric circuit.
8. Voltmeter measures the ____________ ________________ between any two points.
9. For a fixed conductor the graph of V/I is always _____________.
10. Define 1 ohm. State its SI unit.
11. Motion of electrons in an electric circuit constitutes ___________ __________.
12. Motion of electrons through a conductor is retarded by its _________________.
13. A conductor having some appreciable resistance is called a ___________.
14. Resistance of a conductor depends on 4 factors. List them.
15. The resistivity of an alloy is generally ___________ than that of its constituent metals.
16. Both the resistance and resistivity of a material vary with _____________.
17. The equivalent resistance in a series circuit ____________; whereas in a parallel
circuit it _____________. ( increases / decreases)\
18.The current flowing in a parallel circuit ______________ in different resistors.
19.The reciprocal of the equivalent resistance of a group of resistances joined in parallel is equal to the sum of the-a) reciprocals of the individual resistances / b) individual resistances.
(tick the correct one)
20.The work done in moving the charge Q through a potential difference V is ___.
21.The bulbs are usually filled with chemically inactive _________ and __________ gases.
22.The fuse is connected in ____________ with any electric appliance.
23.____________ is the rate of consumption of energy.
24.Formula for electric power P =
25.The electrical energy dissipated in a resistor is given by, W = ____________.
26.The commercial unit of electric energy is _________________, commonly known as ‘unit’.
27.1 kW h = _____________ joule (J)
SECTION A
Choose the correct alternative
1 Electricity constituted by electric charges at rest on the surface of a conductor is called
a Electricity
b Potential difference
c Current electricity
d Static electricity
2 The closed path between two points at different potentials, to make the electric current flow is called
a Electric circuit
b Electric current
c Electric potential
d Electric cell
3 Direction of conventional current is taken from
a Negative to positive
b Positive to negative
c Either
d None of these
4 With increase in temperature, resistance of a conductor,
a Increase
b Decrease
c May increase or decrease
d Resistance of a conductor does not depend on temperature
5 The resistance of straight conductor does not depend upon its
a Shape of cross section
b Temperature
c Material
d Length
6 In series combination resistance increases due to increase in
a Temperature
b Humidity
c Length
d Area of cross section
13
The characteristics of a fuse wire is
a
High melting point
b
Low melting point
c
Low resistivity and high melting point
d
High resistivity and low melting point
SECTION B
14
The unit of resistivity is
a
Ohm/m2
b
Ohm-m
c
Ohm/m3
d
Ohm-m3
15
The length of a conductor is halved. Its conductance will be
a
Halved
b
Unchanged
c
Doubled
d
Quadrupled
16
Three resistors of resistances 10ohm, 5ohm, 2ohm respectively are connected in parallel.
Net resistance will be
a
More than 10ohm
b
Between 10ohm and 5ohm
c
Between 5ohm and 2ohm
d
Less than 2ohm
17
Certain substances lose their electrical resistance at very low temperature. These substances are called
a
Good conductors
b
Semi-conductors
c
Super conductors
18
During the verification of Ohm’s law :
a
ammeter and voltmeter should be connected in series
b
ammeter should be connected in series and voltmeter in parallel
c
ammeter should be connected in parallel and voltmeter in series
d
ammeter and voltmeter should be connected in parallel
19
The rate of flow of an electric charge is known as :
a
electric potential
b
electric conductance
c
electric current
20
Which of the following is not used during the verification of Ohm’s law :
a
Ammeter
b
Voltmeter
c
Galvanometer
d
Rheostat
21
To measure the E.M.F. of a battery and the potential difference (P.D)across a resistor you have the resistor, the battery and some connecting wires. What else do you need?
a
a voltmeter only
b
an ammeter only
c
an ammeter and a voltmeter
d
force meter (newton meter) and a voltmeter
SECTION C
1
Define electric current and state its SI unit
2
Electrons are never stable in any material and keep on moving. What is the need of a battery in an electric circuit?
3
What is voltmeter? How is it connected in a circuit?
4
Why are two wires needed for electrical connection?
5
State ohm s law.
6
Draw a circuit diagram for the verification of ohm’s law. Also plot graphically the variation of current with potential difference.
7
The resistance of a conductor is 1 ohm. What is meant by this statement?
8
a
Why is an ammeter likely to burn out if you connect it in parallel?
8
b
Why a voltmeter has to be connected in parallel to the circuit?
9
a
Why series arrangement is not found satisfactory for domestic lights?
b
What are the advantages of connecting electrical devices in parallel with the battery instead of connecting them in series?
10
Give reason for the following
a
Tungsten is used almost exclusively for filament of electric lamps.
b
Copper and aluminum wires are usually employed for electricity transmission.
c
The elements of heating electrical appliances are made up of an alloy rather than pure metal.
d
Electric fuse is an important component of all domestic circuits.
11
Differentiate overloading and short circuiting.
12
Write a mathematical expression for Joule s law of heating. Name one device which works on this principle
13
Name two factors on which the electric energy consumed by an electrical appliance depends.
14
Name two safety measures commonly used in electric circuits and appliances.
What precautions should be taken to avoid the over loading of domestic electric circuits.
SECTION D
1
The potential difference between the terminals of an electrical iron is 240 V and thecurrent is 5.0 A. What is resistance of the electric iron?
2
a
In an electric circuit with a resistance wire and a cell, the current flowing is I. What would happen to this current if the wire is replaced by another thicker wire of same material and same length. Give reason.
b
What happens to the resistance of a conductor when the length of the conductor is reduced to half?
3
A wire of resistivity ρ is stretched to twice its length. What is its new resistivity?
4
A copper wire of length 2 m and area of cross-section 1.7x10-6 m2 has a resistance of 2 x 10-2ohms. Calculate the resistivity of copper.
5
A wire of resistance 20 ohm is bent in the form of a closed circle. What is the effective resistance between two points at the ends of any diameter of the circle?
6
Two resistors R1 and R2 are connected in parallel. R1 = 2 R2. Compare the current flowing
through these resistors.
7
In an experiment to study the relation between the potential difference across a resistor and the current through it, a student recorded the following observations:
P.D( volt)
1.0
2.2
3.0
4.0
6.4
I (ampere)
0.1
1.2
0.6
0.4
0.6
On examining the above observations the teacher asked the student to reject one set of readings
as the values were out of agreement with the rest. Which one of the above sets of readings can
be rejected? Calculate the mean value of resistance of the resistor based on the remaining four
sets of readings
8
A current of 1 ampere flows in a series circuit containing an electric lamp and a conductor of 5 ohm when connected to a 10 V battery. Calculate the resistance of the electric lamp. Now if a resistance of 10 ohm is connected in parallel with this series combination, what change (if any) in current flowing through 5 ohm conductor and potential difference across the lamp will take place ? Give reason. Draw circuit diagram.
9
Two identical resistors each of resistance 10 ohm are connected to a battery of 6V:
i) in series
ii) in parallel
Calculate the ratio of power consumed in the combination of resistors in the two cases.
10
A TV set shoots out a beam of electron. The beam current is 10 mA. How many electrons strike the TV screen in each second? How much charges strike the screen in a minute?
11
A 40W lamp requires 0.182 A of current at 220 V, while a 60W lamp requires 0.272A of current at 220V. If a 40W lamp and a 60W lamp are connected in series with a 220V line, how much current will flow through each lamp.
12
Draw the circuit consisting of a battery of five 2V cells, 5ohm resistor, 10 ohm resistor, 15 ohm resistor and a plug key. All connected in series. Calculate the current passing through the above circuit when key is closed.
13
Which of the two has greater resistance: a 1 kW heater or a 100 W tungsten bulb, both marked for 230 V?
14
An air conditioner of rating 2000W,220V is operated in a domestic circuit [220V] that has a current rating of 5A. What result do you expect? Justify your answer.
15
A lamp rated 40w and an electric iron rated 800W are used for 6 hours everyday. Calculate the total energy consumed in 30 days.
16
A wire of resistance R is cut into three equal parts.
(i) Find the value of resistance of each part in terms of the original resistance R?
(ii) If these three pieces are connected in parallel, what is the ratio of the resistance so obtained with the original resistance?
Questions based on diagrams ( graphs, circuits, electrical connections)
1 In which position in the circuit should a fuse and a circuit-breaker be connected
Subject: Physics Chapter: 12- Electricity
1. If a net charge Q, flows across any cross-section of a conductor in time t, then the
current I, through the cross-section is ________
2. Electric current is the rate of flow of __________
3. 1ampere = 1____________ / 1_______
4. The charge of an electron is______________
5. The electrons move only if there is a difference of electric pressure – called the
___________ _____________
6. A voltmeter is connected in ________________ and an ammeter in _______________.
7. The ammeter reading ___________ with change in position in the electric circuit.
8. Voltmeter measures the ____________ ________________ between any two points.
9. For a fixed conductor the graph of V/I is always _____________.
10. Define 1 ohm. State its SI unit.
11. Motion of electrons in an electric circuit constitutes ___________ __________.
12. Motion of electrons through a conductor is retarded by its _________________.
13. A conductor having some appreciable resistance is called a ___________.
14. Resistance of a conductor depends on 4 factors. List them.
15. The resistivity of an alloy is generally ___________ than that of its constituent metals.
16. Both the resistance and resistivity of a material vary with _____________.
17. The equivalent resistance in a series circuit ____________; whereas in a parallel
circuit it _____________. ( increases / decreases)\
18.The current flowing in a parallel circuit ______________ in different resistors.
19.The reciprocal of the equivalent resistance of a group of resistances joined in parallel is equal to the sum of the-a) reciprocals of the individual resistances / b) individual resistances.
(tick the correct one)
20.The work done in moving the charge Q through a potential difference V is ___.
21.The bulbs are usually filled with chemically inactive _________ and __________ gases.
22.The fuse is connected in ____________ with any electric appliance.
23.____________ is the rate of consumption of energy.
24.Formula for electric power P =
25.The electrical energy dissipated in a resistor is given by, W = ____________.
26.The commercial unit of electric energy is _________________, commonly known as ‘unit’.
27.1 kW h = _____________ joule (J)
SECTION A
Choose the correct alternative
1 Electricity constituted by electric charges at rest on the surface of a conductor is called
a Electricity
b Potential difference
c Current electricity
d Static electricity
2 The closed path between two points at different potentials, to make the electric current flow is called
a Electric circuit
b Electric current
c Electric potential
d Electric cell
3 Direction of conventional current is taken from
a Negative to positive
b Positive to negative
c Either
d None of these
4 With increase in temperature, resistance of a conductor,
a Increase
b Decrease
c May increase or decrease
d Resistance of a conductor does not depend on temperature
5 The resistance of straight conductor does not depend upon its
a Shape of cross section
b Temperature
c Material
d Length
6 In series combination resistance increases due to increase in
a Temperature
b Humidity
c Length
d Area of cross section
13
The characteristics of a fuse wire is
a
High melting point
b
Low melting point
c
Low resistivity and high melting point
d
High resistivity and low melting point
SECTION B
14
The unit of resistivity is
a
Ohm/m2
b
Ohm-m
c
Ohm/m3
d
Ohm-m3
15
The length of a conductor is halved. Its conductance will be
a
Halved
b
Unchanged
c
Doubled
d
Quadrupled
16
Three resistors of resistances 10ohm, 5ohm, 2ohm respectively are connected in parallel.
Net resistance will be
a
More than 10ohm
b
Between 10ohm and 5ohm
c
Between 5ohm and 2ohm
d
Less than 2ohm
17
Certain substances lose their electrical resistance at very low temperature. These substances are called
a
Good conductors
b
Semi-conductors
c
Super conductors
18
During the verification of Ohm’s law :
a
ammeter and voltmeter should be connected in series
b
ammeter should be connected in series and voltmeter in parallel
c
ammeter should be connected in parallel and voltmeter in series
d
ammeter and voltmeter should be connected in parallel
19
The rate of flow of an electric charge is known as :
a
electric potential
b
electric conductance
c
electric current
20
Which of the following is not used during the verification of Ohm’s law :
a
Ammeter
b
Voltmeter
c
Galvanometer
d
Rheostat
21
To measure the E.M.F. of a battery and the potential difference (P.D)across a resistor you have the resistor, the battery and some connecting wires. What else do you need?
a
a voltmeter only
b
an ammeter only
c
an ammeter and a voltmeter
d
force meter (newton meter) and a voltmeter
SECTION C
1
Define electric current and state its SI unit
2
Electrons are never stable in any material and keep on moving. What is the need of a battery in an electric circuit?
3
What is voltmeter? How is it connected in a circuit?
4
Why are two wires needed for electrical connection?
5
State ohm s law.
6
Draw a circuit diagram for the verification of ohm’s law. Also plot graphically the variation of current with potential difference.
7
The resistance of a conductor is 1 ohm. What is meant by this statement?
8
a
Why is an ammeter likely to burn out if you connect it in parallel?
8
b
Why a voltmeter has to be connected in parallel to the circuit?
9
a
Why series arrangement is not found satisfactory for domestic lights?
b
What are the advantages of connecting electrical devices in parallel with the battery instead of connecting them in series?
10
Give reason for the following
a
Tungsten is used almost exclusively for filament of electric lamps.
b
Copper and aluminum wires are usually employed for electricity transmission.
c
The elements of heating electrical appliances are made up of an alloy rather than pure metal.
d
Electric fuse is an important component of all domestic circuits.
11
Differentiate overloading and short circuiting.
12
Write a mathematical expression for Joule s law of heating. Name one device which works on this principle
13
Name two factors on which the electric energy consumed by an electrical appliance depends.
14
Name two safety measures commonly used in electric circuits and appliances.
What precautions should be taken to avoid the over loading of domestic electric circuits.
SECTION D
1
The potential difference between the terminals of an electrical iron is 240 V and thecurrent is 5.0 A. What is resistance of the electric iron?
2
a
In an electric circuit with a resistance wire and a cell, the current flowing is I. What would happen to this current if the wire is replaced by another thicker wire of same material and same length. Give reason.
b
What happens to the resistance of a conductor when the length of the conductor is reduced to half?
3
A wire of resistivity ρ is stretched to twice its length. What is its new resistivity?
4
A copper wire of length 2 m and area of cross-section 1.7x10-6 m2 has a resistance of 2 x 10-2ohms. Calculate the resistivity of copper.
5
A wire of resistance 20 ohm is bent in the form of a closed circle. What is the effective resistance between two points at the ends of any diameter of the circle?
6
Two resistors R1 and R2 are connected in parallel. R1 = 2 R2. Compare the current flowing
through these resistors.
7
In an experiment to study the relation between the potential difference across a resistor and the current through it, a student recorded the following observations:
P.D( volt)
1.0
2.2
3.0
4.0
6.4
I (ampere)
0.1
1.2
0.6
0.4
0.6
On examining the above observations the teacher asked the student to reject one set of readings
as the values were out of agreement with the rest. Which one of the above sets of readings can
be rejected? Calculate the mean value of resistance of the resistor based on the remaining four
sets of readings
8
A current of 1 ampere flows in a series circuit containing an electric lamp and a conductor of 5 ohm when connected to a 10 V battery. Calculate the resistance of the electric lamp. Now if a resistance of 10 ohm is connected in parallel with this series combination, what change (if any) in current flowing through 5 ohm conductor and potential difference across the lamp will take place ? Give reason. Draw circuit diagram.
9
Two identical resistors each of resistance 10 ohm are connected to a battery of 6V:
i) in series
ii) in parallel
Calculate the ratio of power consumed in the combination of resistors in the two cases.
10
A TV set shoots out a beam of electron. The beam current is 10 mA. How many electrons strike the TV screen in each second? How much charges strike the screen in a minute?
11
A 40W lamp requires 0.182 A of current at 220 V, while a 60W lamp requires 0.272A of current at 220V. If a 40W lamp and a 60W lamp are connected in series with a 220V line, how much current will flow through each lamp.
12
Draw the circuit consisting of a battery of five 2V cells, 5ohm resistor, 10 ohm resistor, 15 ohm resistor and a plug key. All connected in series. Calculate the current passing through the above circuit when key is closed.
13
Which of the two has greater resistance: a 1 kW heater or a 100 W tungsten bulb, both marked for 230 V?
14
An air conditioner of rating 2000W,220V is operated in a domestic circuit [220V] that has a current rating of 5A. What result do you expect? Justify your answer.
15
A lamp rated 40w and an electric iron rated 800W are used for 6 hours everyday. Calculate the total energy consumed in 30 days.
16
A wire of resistance R is cut into three equal parts.
(i) Find the value of resistance of each part in terms of the original resistance R?
(ii) If these three pieces are connected in parallel, what is the ratio of the resistance so obtained with the original resistance?
Questions based on diagrams ( graphs, circuits, electrical connections)
1 In which position in the circuit should a fuse and a circuit-breaker be connected
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