SEE Science (Electricity and Magnetism) Notes
Electricity and Magnetism
1. Write three differences between fuse wire and phase wire.
Ans: differences between fuse and phase wire are:
S.N
|
Fuse wire
|
S.N
|
Phase wire
|
a)
|
It has low melting point.
|
a)
|
It has high melting point.
|
b)
|
It is made of alloy of tin and lead.
|
b)
|
It is usually made of copper or
aluminum.
|
c)
|
It breaks the circuit during excess
flow of electricity.
|
c)
|
It carries the current from the source
to the device.
|
2. Which principle is dynamo based on?
Ans: Dynamo is based on the principle of electro-magnetic
induction.
3. What is parallel combination of cells?
Ans: The combination of
cells in which the positive terminals of all the cells are connected together
at one common point and negative terminals of all the cells at another common
point is called parallel combination of cells.
4. What is lighting effect of current?
Ans: When electric
current is passed through some electric appliances, they changes electric
energy in to light energy. This effect of current is called lighting effect of
current.
5. What is transformer? In what principle does it based. And
write its type.
Ans: A transformer is a device to convert low A.C. voltage
into high A.C voltage and vice versa.
It
is based on the principle of 'Mutual Induction'.
Its
types are:
a) Step-up transformer
b)
6. What is Fleming's right hand rule state?
Ans: Fleming's right
hand rule state that," When the thumb, the four finger and middle finger of the
right hand are stretched mutually perpendicular to each other than the thumb shows direction of motion
of conductor, four finger shows the direction of magnetic field and the middle
finger shows the direction of induced current.
7. What is short circuit?
Ans: A faulty
or accidental connection between two points of different potential in an
electric circuit, bypassing the load and establishing a path of low resistance
through which an excessive current can flow.
Or
Short-circuiting
is the condition in which the neutral wire and live wire touches each other
directly without any load.
8. Write any four ways of increasing electricity produced from
a dynamo or a generator.
Ans: Ways of increasing
electricity produced from a dynamo or a generator are:
a) By increasing the number of turns in the coil.
b) By increasing the strength of magnetic field.
c) By decreasing the distance between the coil and the magnet.
d) By increasing the speed of rotation of the coil.
9. What is over loading?
Ans: Using too many electrical appliances at a time and
drawing excessive power from an electric circuit is called overloading.
10. Write any two characteristic of fuse wire.
Ans: Characteristics of fuse wire are:
a) Low melting point.
b) High resistance.
c) It is made of tin (63%) and lead (37%) alloy.
d) It breaks the circuit during excess flow of electricity.
11. Which material is used to make main switch box in domestic
electric circuit, why?
Ans: Thermosetting plastic is used to make main switch box
in domestic electric circuit because it does not melt on heating and acts as
insulator so that electric shock can be avoided.
12. Why 220V is written in most of the electrical appliances?
Ans: 220V is written in most of the electrical appliances
because most of the electrical appliances work at the potential difference of
220V.
13. Parallel connection is used in domestic circuits. List any
three advantages of it.
Ans: Advantages of using Parallel connection in domestic
circuits are:
a) In this connection, each individual appliance can be
controlled separately.
b) Although one or more appliance fails, it will not affect the
working of remaining appliance.
c) By increasing or reducing the number of appliance, the
efficiency of remaining appliances are not affected.
14. A coil made of insulated copper wire is connected to a
galvanometer. what happen to the deflection of the galvanometer if this coil is moved towards a stationary
bar magnet and then move away from it? Give reason. Name the phenomenon
involved.
Ans: If the coil is moved towards a stationary bar magnet,
there is a momentary deflection of the galvanometer pointer indicating a flow of
current. But when coil is moved away from it, there is another momentary
deflection of the galvanometer pointer in the opposite direction. It is due to
the relative motion between the coil and the magnet.
This phenomenon is known as electro-magnetic induction.
15. Write two differences
between generator and electric motor.
Ans: Differences
between generator and electric motor are:
S.N
|
Generator
|
S.N
|
Electric motor
|
a)
|
It converts mechanical energy into
electrical energy.
|
a)
|
It converts electrical energy into
mechanical energy.
|
b)
|
It works on the principle of
electro-magnetic induction.
|
b)
|
It works on the principle of motor
effect.
|
c)
|
It is used in hydropower stations.
|
c)
|
It is used in domestic appliances
such an electrical fan, washing machine etc.
|
16. The coil of transformer is coated by enamel, why?
Ans: Coil of transformer is coated by enamel because
a) It protects the transformer from being heated.
b) It protects and prevents the loss of energy due to eddy
current.
17. Write a difference between electricity generating by
generator and cell.
Ans: Difference between electricity generating by generator
and cell are:
S.N
|
Electricity generating by generator
|
S.N
|
Electricity generating by cell
|
a)
|
It produces alternating current (AC).
|
a)
|
It produces direct current (DC).
|
18. Write one function of mercury vapour and fluorescent powder
in fluorescent lamp.
Ans: Function of mercury vapour in fluorescent lamp is
a) To produce ultraviolet rays (UV rays) when electron from
cathode strike the mercury atoms.
Function of fluorescent powder in fluorescent lamp is
b) When electrons from cathode strike the mercury atoms, UV
rays are produced. The UV rays when strike the fluorescent powder produces
visible light. Hence, in order to produce visible light the inner wall of
fluorescent lamp is coated with fluorescent powder.
19. Write a unit of electric power consumed.
Ans: A unit of electric power consumed is kilowatt-hour
(kWh).
20. Write the main two reasons for use of filament of tungsten
wire in on electric bulb.
Ans: Reasons for use of filament of tungsten wire in on
electric bulb are:
a) It has high resistance.
b) It has high melting point (about 34000C).
21. Write three laws of Michael Faraday's electromagnetic
induction.
Ans: Laws of Michael Faraday's electromagnetic induction
are:
a) Whenever there is change in the magnetic flux linked with
the closed circuit, an e.m.f. is induced in the circuit.
b) The induced e.m.f. lasts as long as the change in the
magnetic flux continues in the circuit.
c) The magnitude of induced e.m.f. is directly proportional to
the rate of change of magnetic flux linked with the circuit.
22. What is an electric circuit?
Ans: The path of the electricity through which it flows to
conduct various types of electric appliances is called electric circuit.
23. Why is a fuse connected in a domestic electric circuit?
Ans: A fuse is connected in a domestic electric circuit
because to prevent the electrical appliances from getting damage due to over
flow of electrical current.
24. In what effect of electricity is an electric bell based?
Ans: An electric bell is based on magnetic effect of
current.
25. Write any one difference in the construction of step up and
step down transformers.
Ans: Difference in the construction of step up and step down
transformers are:
26. Write formula of relation between current, potential
difference and power.
Ans: Relation between current, potential difference and
power is
Power =
Current
Potential
difference
i.e. P = I
V
27. What is motor effect?
Ans: The turning effect produced in a current carrying
conductor when placed in a magnetic field is called motor effect.
28. Write the name of any two devices which is based on motor
effect.
Ans: Devices based on motor effect are:
a) Electric motor
b) Electric fans
c) Washing machine
29. What is fuse wire? Which alloy is used to make it?
Ans: A fuse wire is a
short metal wire, having low melting point, made of an alloy of tin and lead.
It is
made of an alloy of tin (63%) and lead (37%).
30. Write two differences between electric generator and
electric motor.
Ans: Ans: Differences between electric generator and
electric motor are:
S.N
|
Electric generator
|
S.N
|
Electric motor
|
a)
|
It converts mechanical energy into
electrical energy.
|
a)
|
It converts electrical energy into
mechanical energy.
|
b)
|
It works on the principle of
electro-magnetic induction.
|
b)
|
It works on the principle of motor
effect.
|
c)
|
Electromagnet is use in electric
generator.
|
c)
|
Permanent magnet is used in electric.
|
31. Write two differences between AC and DC.
Ans: Differences between A.C. and D.C. are:
S.N
|
A.C.
|
S.N
|
D.C.
|
a)
|
The current that changes its polarity
and magnitude at a certain interval of time is called alternating current
(A.C.).
|
a)
|
The current that does not change its
polarity and magnitude at a certain interval of time is called direct current
(D.C.).
|
b)
|
A.C. voltage can be altered by
transformer.
|
b)
|
D.C. voltage cannot be altered by
transformer.
|
c)
|
It is generated by A.C. generator.
|
c)
|
It is generated by battery and
dynamo.
|
32. What is electromagnetic induction?
Ans: Whenever there is
change in the magnetic flux linked with the closed circuit, an e.m.f. is induced
in the circuit called induce e.m.f. This phenomenon is called electromagnetic
induction.
Or
The phenomenon by which electric current is produced in a
closed coil due to the relative motion between the coil and the magnet is
called electromagnetic induction.
33. What type of wire is used in an electric heater? Why?
Ans: Nichrome wire is used in an electric heater because
a) It has high resistance.
b) It has high melting point (about 9000C).
34. Write the uses of step-up transformer.
Ans: The uses of step-up transformer are:
a) It is used in electric grids to save electrical energy
during power transmission through overhead wire.
b) Step-up transformers are used in television, X-ray's tubes,
discharge tubes, etc.
35. Write the uses of step-down transformer.
Ans: The uses of step-down transformer are:
a) It is used at power sub-stations to step down the voltage
before its distribution to consumers.
b) Step-down transformers are used in electric bells, radio
sets, transistors, battery chargers, etc.
36. Write Fleming's left hand rule.
Ans: Fleming's left hand rule state that," When the
thumb, the four finger and middle finger of the right hand are stretched
mutually perpendicular to each other than the thumb shows direction of motion
of conductor, four finger shows the direction of magnetic field and the middle
finger shows the direction of electric current in conductor.
37. What types of loads are arranged in domestic electric
circuit is more effective? Mention one advantage of this arrangement.
Ans: Loads are connected in parallel in domestic wiring. Its
advantages are
a) In parallel connection of loads, every load can be operated
separately according to our will.
b) In such connection, if one of the loads is damaged, remaining
load can be operated.
38. The fluorescent lamp with power 60watt gives more brightness
than the filament lamp with the same
power, why?
Ans: Filament lamp converts only 10% of the electrical
energy into light energy but fluorescent lamp converts 30% of the electrical
energy into light energy. Therefore, the fluorescent lamp with power 60watt
gives more brightness than the filament lamp with the same power.
39. What is meant by frequency of electricity is 50Hz?
Ans: The frequency of electricity is 50Hz which means that,
the coil of AC generator is rotated at the rate of 50 revolutions per second.
40. What is heating element?
Ans: Heating element is the wire having very high melting
point and resistivity which is used in electrical heating appliances to convert
electrical energy into heat energy.
41. In electroplating process the object on which electroplating
is to be done, must be made cathode, why?
Ans: During electroplating, the positively charged ions
become neutral by gaining electrons and are deposited on cathode. Therefore,
the object on which electroplating is to be done, must be made cathode in
electroplating.
42. On what two principles the transformer is based?
Ans: Two principles the transformer is based are:
a) The input energy is equal to the output energy in the
transformer. i.e. I1V1 = I2V2.
b) Voltage is directly proportional to the number of turns of
the wire in the coil of the transformer.
43. "The use of alternating current would be limited, if
the transformer was not invented." Prove the statement.
Ans: "The use of alternating current would be limited,
if the transformer was not invented." It is because
a) The conversion of low AC voltage into high AC voltage in the
power stations would be impossible.
b) It would be impossible to operate the electric appliances
which require a low AC voltage.
44. Write two differences between filament and fluorescent lamp.
Ans: Differences between filament and fluorescent lamp are:
S.N
|
Fluorescent lamp
|
S.N
|
Filament lamp
|
a)
|
Fluorescent lamp converts 30% of the
electrical energy into light energy.
|
a)
|
Filament lamp converts only 10% of
the electrical energy into light energy
|
b)
|
It is filled with mercury vapour.
|
b)
|
It is filled with inert gases like
Nitrogen, Argon etc.
|
c)
|
Its average lifespan is about 3000
hours.
|
c)
|
Its average lifespan is about 1000
hours.
|
d)
|
Fluorescent powder emits light.
|
d)
|
Tungsten filament emits light.
|
45. What is the full form
of CFL? How does the use of CFL bulbs minimize load shedding?
Ans: CFL – Compact Fluorescent Lamp
CFL converts 30% of total electrical energy into light energy. So, it
consumes less energy than that of other ordinary bulbs. Due to this reason, the
use of CFL bulbs minimizes load shedding.
46. What is fuse?
Ans: A thin piece of
wire made up of an alloy of tin and lead, used as a safety device to prevent the
excessive electric current beyond the current rating is called fuse.
47. What is current rating and electric power?
Ans: The maximum current that can be passed through the wire
with safety is called current rating.
The electric power of a device is
the rate at which it converts electrical energy into other forms.
48. What types of connection of bulb is done in domestic
electric circuit? Mention the advantages of this arrangement.
Ans: Bulbs are connected in parallel in domestic wiring. Its
advantages are
a) In parallel connection of bulbs, every bulb can be operated
separately according to our will.
b) In such connection, if one of the bulbs is damaged,
remaining bulb can be operated.
c) There is no change in the brightness of bulb if extra bulbs
are added or removed in a circuit.
49. Differences between parallel connection and series
connection of cells.
Ans: Differences between parallel connection and series
connection are:
S.N
|
Parallel connection of cells
|
S.N
|
Series connection of cells
|
a)
|
The combination of cells in which the
positive terminals of all the cells are connected together at one common
point and negative terminals of all the cells at another common point is
called parallel combination.
|
a)
|
The combination of cells in which
positive terminal of one cell is connected to the negative terminal of the
second cell and so on is called series combination.
|
b)
|
It provides current for long time.
|
b)
|
It provide more current or voltage at
a time.
|
c)
|
It has fixed e.m.f.
|
c)
|
Its e.m.f. is changeable.
|
50. Write the use of electromagnetic induction.
Ans: Use of electromagnetic induction is:
a) Generator is made by using this process.
51. What is filament? Which material is used as filament? Give
two reasons.
Ans: The thin wire, usually tungsten, inside a light
bulb that emits light when heated to a high temperature by an electric current
Tungsten coil is used as filament because
a) It has high melting point
b) It has high resistance which converts electric energy easily
into light energy.
52. Why inert gas is filled in the filament?
Ans: Inert gas like argon, neon, nitrogen etc. are filled in
the filament to prevent the filament made up of tungsten from oxidation and evaporation
when heated to a high temperature.
53. Differences between step-up and step-down transformer.
Ans: Differences between step-up and step-down transformer
are:
S.N
|
Step-up transformer
|
S.N
|
Step-down transformer
|
a)
|
It converts low AC voltage into high
AC voltage.
|
a)
|
It converts high AC voltage into low
AC voltage.
|
b)
|
Number of turns in secondary coil is
more than that in primary coil.
|
b)
|
Number of turns in secondary coil is
less than that in primary coil.
|
c)
|
The primary voltage is less than the
secondary voltage.
|
c)
|
The primary voltage is more than the
secondary voltage.
|
54. Why fuse is connected in live line?
Ans: When the current in the circuit exceeds the specific
value, the fuse wire gets heated up to the extent that it melts and breaks the
circuit so that electrical appliances and life remain safe. Therefore, fuse is
connected in live line.
55. What is earthing? Differences between parallel and series
combination.
Ans: The process of connecting the conducting wire from the
metallic body of an electrical appliance to the certain depth of the earth to
prevent from electric shock is called earthing.
S.N
|
Series combination
|
S.N
|
Parallel combination
|
a)
|
It can provide more current or
voltage.
|
a)
|
It can provide constant current.
|
b)
|
It is used when current of large
amount is
required
|
b)
|
It is used when current is required
for long time.
|
56. Point should be remembered in household remaining.
Ans: a) The live wire
should have brown/red insulation, the neutral wire with blue/black insulation
and the earth wire with green/yellow striped green insulation.
b) Switches and fuses
should be connected with live line.
c) Appropriate fuses
should be used.
d) Separate fuses
should be used in every flat or room.
e) Separate switches
should be used for each electrical appliance.
f) Wiring should not be
done in damp area or in the region where water leaks.
g) Heavy electrical
appliances should be earthed properly.
57. The number turns in the primary
coil and secondary coil of a transformer are never made equal.
Ans: A transformer is used to
convert a low AC voltage into high AC voltage and vice versa. If the number of
turns in primary coil and secondary coil is made equal then the transformer
neither increase nor decreases the output AC voltage. Hence, the number of
turns in primary coil and secondary coil of a transformer are never made equal.
58. Differences between Nichrome wire and fuse
wire.
Nichrome wire
|
Fuse wire
|
1. It has a high melting point.
|
1. It has a low melting point
|
2. It has high resistivity
|
2. It has low resistivity
|
59.
Study the given figure
and answer the following questions:
i) The given figure shows which effect of
electricity?
Ans: The given figure shows
chemical effect of current electricity.
ii) Which metal plate should be used as anode?
Ans: Copper plate should be
used as anode.
60.
Study the given figure
and answer the following questions:
a) Which type of transformer is this why?
b) Which function does the core do in
transformer?
Ans: a) It is a step-down transformer
because the number of turns in the secondary coil
is less than that in the
primary coil.
b) The core of transformer converts high
voltage AC into low voltage AC.
61. Draw a diagram showing the electroplating of copper on iron
nail. Also, write down the reaction that takes place at cathode and anode.
62. 1Kilo Watt (kW) = 1000W
1 Mega Watt (MW) =
1000000W
1 Horse power (H.P.) =
746W (approx. 750W)
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