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(22)508-RR(A) [ Turn over

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KARNATAKA SECONDARY EDUCATION EXAMINATION BOARD, MALLESWARAM, BANGALORE – 560 003

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MODEL ANSWERS

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Date : 22. 06. 2019 ] CODE NO. : 71

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Subject : ELEMENTS OF MECHANICAL AND ELECTRICAL ENGINEERING-2

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Qn. Nos.

Sub. Qn.No. Value Points Marks

SECTION - A 1. a) Explain the functions of piston in an I.C. engine. 2

Ans.

Piston : It is a reciprocating part of the engine and

reciprocates to and fro inside the cylinder. The top of

the piston is suitable cavity and the lower part of the

piston is connected with connecting rod with the help

of a pin called as gudgeon pin.

2

A CCE RR REVISED

71 2 CCE RR

(22)508-RR(A)

Qn. Nos.


b) List the main applications of I.C. engines. 3

Ans.

Applications of I.C. engine are —

i) vehicles, locomotives, ships and aircrafts

ii) used for power generation

iii) used in farm tractors, lawn movers, concrete

mixing devices and motor boats

iv) used in agricultural applications.

3 × 1 = 3

c) Draw a neat sketch of four stroke diesel engine and

explain briefly. 5

Ans.

Four stroke diesel engine :

Diesel engine operates on diesel cycles and is operated

with diesel fuels. These engines are also called as

compression ignition engines. These engines do not

require ignition system, only air is admitted during

suction stroke and diesel fuel is injected with the help

of a suitable injector in to the compressed air within

the engine cylinder and air-fuel mixing takes place

inside the engine cylinder operates with higher

compression ratio and consumes less fuel.

Sketch = 3

Explanation = 2

5

CCE RR 3 71


Qn. Nos.


2. a) Name the two types of air compressor. 2 Ans. i) Reciprocating air compressor ii) Centrifugal air compressor.

2 × 1 = 2

b) Explain the applications of air compressor. 3

Ans.

Applications of air compressor :

i) inflating tubes and tyres

ii) inflating baloons

iii) used in automobile workshop

iv) used in hospitals

v) used in painting industries

vi) used in bore well rigging machines.

3 × 1 = 3

c) Draw a neat sketch of single stage reciprocating air

compressor and label the parts. 5

Ans.

Single stage reciprocating air compressor.

Sketch = 3

Parts = 2

5

3. a) Mention the applications of air conditioning. 2

Ans.

Applications of Air Conditioning :

i) residential air conditioning : homes, hospitals,

auditoriums, theatres etc.

71 4 CCE RR

(22)508-RR(A)

Qn. Nos.


ii) commercial air conditioning : storage of foods and

other commodities, special applications

iii) industrial air conditioning : chemical, electronic,

tobacco, textile and software industries.

2 × 1 = 2

b) Explain the following properties of good refrigerant : 3

i) Stability

ii) Non-flammability

iii) Safety.

Ans.

Stability : refrigerant should be chemically

stable, non-toxic and inert.

Non-flammability : it should be non-explosive and

should not cause any fire hazard.

Safety : it should not corrode the parts or

materials used in construction

where it is passed through and

should not react with lubricating

oil.

3 × 1 = 3

c) Draw a neat sketch of winter air conditioning system

and label the parts. 5

Ans.

Winter Air conditioning system.

Sketch = 3

Parts = 2

5

CCE RR 5 71


Qn. Nos.


4. a) List out the work holding devices on a lathe. 2

Ans.

i) centres

ii) carriers and catch plates

iii) chucks

iv) face plates

v) mandrels.

4 × ½ = 2

b) What are the operations which are performed on the

lathe by holding the job in between the centres by

chuck ? 3

Ans.

Turning, facing, chamfering, parting, grooving,

knurling, thread cutting, polishing.

3 × 1 = 3

c) Calculate the half taper angle for taper turning by tail-

stock offset method when larger diameter is 30 mm

and smaller diameter is 25 mm and length of taper is

50 mm. 5

Ans.

Taper of conicity = D − d

l

Half taper angle = D − d

2l

Set over(s) = 1 × half taper angle

Set over(s) 1 × 30 − 25

2 × 50

Set over(s) =

5100

= 0 ⋅ 05

Formula = 2

Substitution = 2

Result = 1

5

OR

71 6 CCE RR

(22)508-RR(A)

Qn. Nos.


a) Name the differential types of milling cutters. 2

Ans.

Plain milling cutter, Side milling cutter, Angle milling

cutter, End milling cutter, slot milling cutters.

4 × ½ = 2

b) What do you understand by up-milling and down-

milling ? Explain. 3

Ans.

Up-milling : it is also called as conventional milling in

which the direction of rotation of cutter and the feed

are in the opposite directions.

Down-milling : It is also called as climb milling in which

the directions of rotation of cutter and the feed are in

the same direction.

1½ +1½ = 3

c) A 25 mm thick M.S. plate is to be drilled 25 mm drill

with a cutting speed 25 m/min during the operation.

How much spindle speed is to be adopted ? 5

Ans.

d = 25 mm = 0·025 m, t = 25 mm = 0·025 m

v = 25 m/min

1000dNv π= m/min

N =

1000 vπd

= 1000 × 25π × 25

= 318 RPM

Formula = 2

Substitution = 2

Result = 1

5

CCE RR 7 71


Qn. Nos.


5. a) What is brazing ? 2 Ans. Brazing : it is a process of joining two metal pieces with the help of non-ferrous filler metal at a comparatively higher temperature of about more than 450˚C. This process is most suitable for joining dissimilar metal and filler rod used must be made up of non-ferrous metal — commonly used fluxes are borax fluorides, chlorides and boric acid.

2

b) Explain the advantages of soldering. 3 Ans. Advantages of soldering : i) dissimilar metals can be joined ii) it is simple low cost, flexible, economical, and user

friendly iii) The life of solder will be more iv) Low amount of power is required to heat the

soldering iron v) The soldering can be done at low temperature and

controlling is very easy vi) soldered joints can be dismantled.

3 × 1 = 3

c) Draw a neat sketch showing all the equipment of metal arc welding. 5 Ans.

Equipment of metal arc welding.

Sketch = 4 Parts = 1

5

71 8 CCE RR

(22)508-RR(A)

Qn. Nos.


SECTION – B

6. a) Define statically induced emf. 2 Ans. The e.m.f. induced in a conductor due to variations of flux linking with conductor, when both the magnetic field and the conductor are stationary is called the statically induced e.m.f.

2

b) Explain Fleming’s right hand rule. 3 Ans. Fleming’s right hand rule : Stretch the fore finger and the thumb of your right hand at right angles to each other. The fore finger indicates the direction of flux, the thumb indicates motion of the conductor and middle finger indicates the direction of e.m.f. induced in the conductor.

3

c) Draw a neat sketch of self induced emf and explain it briefly. 5 Ans.

Self induced e.m.f. sketch

The e.m.f. induced in a coil due to changing flux created the current flowing through the same coil is called self induced e.m.f. This is always in opposition to the applied voltage and is measured in volts. Sketch = 3 Explanation = 2

5

CCE RR 9 71


Qn. Nos.


7. a) Define form factor. 2

Ans.

It is defined as the ratio of r.m.s. value to average value

of an alternating quantity.

Form factor =

r.m .s. valueaverage value

= 0 ⋅ 7070 ⋅ 637

= 1 ⋅11

2

b) Describe power and power factor of an a.c. circuit. 3

Ans.

Power : power consumed by a single phase a.c. circuit

is given by the product of the applied voltage to the

circuit and the in phase component of current in the

circuit. It is expressed in watts or kilowatts.

Power factor : cosine of the angle ( φ) between applied

voltage and the total current in the circuit is called

power factor of that circuit.

Power factor = cos φ

2 × 1½ = 3

c) Draw a neat diagram of sinusoidal waveform and mark

the following : 5

i) negative

ii) amplitude

iii) positive.

Ans.

Sketch = 2

Marking = 3

5

71 10 CCE RR

(22)508-RR(A)

Qn. Nos.


8. a) What is transformer ? 2

Ans.

Transformer is a static electromagnetic device which

transfers electrical energy from one ac circuit to

another circuit either at the same voltage or at a

different voltage but at the same frequency.

2

b) Explain the working principle of d.c. motor. 3

Ans.

A dc motor works on the principle that whenever a

current carrying conductor is placed in a magnetic field

it experiences a force and tends to move at right angle

to the direction of the main field.

The direction of rotation of the conductor is determined

by Fleming’s left hand rule.

F = BLI newtons

B = flux density measure in Wb 2m/

L = Length of the conductor in m

I = current in the conductor in amps.

3

c) How does the step-up transformer differ from step-

down transformer ? 5

Ans.

CCE RR 11 71


Qn. Nos.


If the transformer takes power at a lower voltage and delivers power at a higher voltage it is called step-up transformer.

212121 , , IIEENN ><<

Step-down transformer

When the transformer takes power at a higher voltage

and delivers power at a lower voltage it is called step-

down transformer.

121212 , , IIEENN ><<

2 × 2 = 5

OR

a) What is d.c. generator ? 2 Ans. DC generator is electromagnetic machine which converts mechanical energy into electrical energy.

2

b) Explain squirrel cage induction motor. 3

Ans.

Explanation

71 12 CCE RR

(22)508-RR(A)

Qn. Nos.


Squirrel cage rotor, rotor windings consist of

aluminium or copper bars of rectangular cross-section

moulded into the slots of the rotor core. These bars are

shorted at both ends by thick copper rings. The rotor

winding appears as a cage and hence it is called

squirrel cage induction motor.

3

c) How does the d.c. series generator differ from d.c.

shunt generator ? 5

Ans.

It is a self existed DC generator in which the field

winding is connected in series with the armature

winding. Field winding has less number of turns of

thick wire and has low resistance.

It is a self excited dc generator in which the field

windings are connected parallel with the armature

winding. Field winding has more number of turns of

thin wire and has high resistance.

2 × 2½ = 5

CCE RR 13 71


Qn. Nos.


9. a) Explain thermostat. 2

Ans.

Thermostat controls the operation of most of the

heating appliances acting as a switch it connects to a

bi-metal strip.

2

b) Mention the parts of electric stove. 3

Ans.

Parts of Electric stove :

i) Metal body or Frame

ii) Heater plate made of china clay or porcelain

iii) Heating element is made of nichrome wire

iv) Terminals with nuts and washers

v) Porcelain bushes for terminal

vi) Supply cord, plug top and connector.

6 × ½ = 3

c) Draw a neat sketch of a.c. ceiling fan and label the

parts. 5

Ans.

A.C. ceiling fan sketch and parts

Sketch = 3

Parts = 2

5

71 14 CCE RR

(22)508-RR(A)

Qn. Nos.


10. a) Explain the heating element of electric iron. 2

Ans.

Heating element is made of nichrome strip wound on

the mica piece and insulated with mica on both sides

which is kept under the pressure plate.

2

b) Differentiate between diode and transistor. 3

Ans.

Diode : It is a two element semiconductor device

formed by joining a piece of P-type semiconductor to a

piece of N-type semiconductor by a suitable technique.

Transistor : Transistor is a three terminal

semiconductor device formed by sandwiching a layer of

one type of semiconductor ( P or N ) in between two

layers of another type of semiconductor ( N or P ).

1½ × 2 = 3

c) Draw a neat sketch of reverse bias of a P-N junction

diode and explain it briefly. 5

Ans.

When an external voltage source is applied to the diode

such that the positive terminal of the battery is

CCE RR 15 71


Qn. Nos.


connected to N-type semiconductor and the negative

terminal to a P-type semiconductor the diode is said to

be reverse biased.

Sketch = 2½

Explanation = 2½

5

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