CBSE Class 12 Electrical Machines Question Paper 2020

H$moS> Z§.
Code No. 311
amob Z§. narjmWu H$moS >H$mo CÎma-nwpñVH$m Ho$ _wI-n¥ð
Roll No. >na Adí` {bIo§ &
Candidates must write the Code on the
title page of the answer-book.

ZmoQ> NOTE
(I) H¥$n`m Om±M H$a b| {H$ Bg àíZ-nÌ _o§ _w{ÐV (I) Please check that this question
n¥ð> 11 h¢ & paper contains 11 printed pages.

(II) àíZ-nÌ _| Xm{hZo hmW H$s Amoa {XE JE H$moS (II) Code number given on the right
>Zå~a H$mo N>mÌ CÎma-nwpñVH$m Ho$ _wI-n¥ð> na hand side of the question paper
{bI| & should be written on the title page of
the answer-book by the candidate.
(III) H¥$n`m Om±M H$a b| {H$ Bg àíZ-nÌ _| (III) Please check that this question
>28 àíZ h¢ & paper contains 28 questions.
(IV) H¥$n`m àíZ H$m CÎma {bIZm ewê$ H$aZo go (IV) Please write down the Serial
nhbo, CÎma-nwpñVH$m _| àíZ H$m H«$_m§H$ Number of the question in the
Adí` {bI| & answer-book before attempting it.
(V) Bg àíZ-nÌ H$mo n‹T>Zo Ho$ {bE 15 {_ZQ >H$m (V) 15 minute time has been allotted to
g_` {X`m J`m h¡ & àíZ-nÌ H$m {dVaU read this question paper. The
nydm©• _| 10.15 ~Oo {H$`m OmEJm & question paper will be distributed
10.15 ~Oo go 10.30 ~Oo VH$ N>mÌ Ho$db at 10.15 a.m. From 10.15 a.m. to
10.30 a.m., the students will read the
àíZ-nÌ H$mo n‹T>|Jo Am¡a Bg Ad{Y Ho$ Xm¡amZ question paper only and will not
do CÎma-nwpñVH$m na H$moB© CÎma Zht {bI|Jo & write any answer on the
answer-book during this period.

{dÚwV² _erZ| (g¡ÕmpÝVH$)
ELECTRICAL MACHINES (Theory)

{ZYm©[aV g_` : 2 KÊQ>o A{YH$V_ A§H$ : 40
Time allowed : 2 hours Maximum Marks : 40

.311 1 P.T.O.

IÊS> H$
^mJ I

{H$Ýht Xg àíZm| Ho$ CÎma Xr{OE & 110=10

1. e{º$ n[aUm{_Ì H$s bmoh H$moa b¡{_ZoQ> H$s OmVr h¡ 1
(A) {hñQ>oao{gg hm{Z H$_ H$aZo Ho$ {bE
(B) ^§da Ymam hm{Z H$_ H$aZo Ho$ {bE
(C) Vm_« hm{Z H$_ H$aZo Ho$ {bE
(D) Cn`w©ŠV (A) Ed§ (B) Ho$ H$maU

2. EH$ n[aUm{_Ì _|, {ZåZ{b{IV dmB§qS>J H$m AZwàñW-H$mQ> joÌ\$b A{YH$ hmoVm h¡ : 1
(A) àmW{_H$ dmB§qS>J
(B) {ÛVr`H$ dmB§qS>J
(C) Cƒ dmoëQ>Vm dmB§qS>J
(D) {ZåZ dmoëQ>Vm dmB§qS>J

3. e{ŠV n[aUm{_Ì H$s bmoh H$moa H$m AZwàñW-H$mQ> bJ^J Jmobr` hmoVm h¡ & Eogm Bg{bE
{H$`m OmVm h¡ Š`m|{H$ 1
(A) Jmob H$moa H$mo Omo‹S>Zm AmgmZ hmoVm h¡ &
(B) Jmob Hw§$S>br ~ZmZm AmgmZ hmoVm h¡ &
(C) {dÚwV²-Mwå~H$s` ~b Hw§$S>br H$mo Jmob H$aZo H$m à`mg H$aVo h¢ &
(D) Cn`w©ŠV g^r Ho$ H$maU

4. ~hþV H$_ ^ma na `{X {XîQ> Ymam grarµO _moQ>a H$m joÌ n[anW Iwb OmVm h¡, V~ 1
(A) _moQ>a H$s Mmb ~hþV A{YH$ hmo OmEJr &
(B) _moQ>a Yr_r MbZo bJoJr &
(C) _moQ>a éH$ OmEJr &
(D) _moQ>a gm_mÝ` ê$n go MbVr ahoJr &

.311 2

SECTION A
PART I

Attempt any ten questions. 110=10

1. Iron core of a power transformer is laminated 1
(A) To reduce hysteresis loss
(B) To reduce eddy current loss
(C) To reduce copper loss
(D) Due to (A) and (B) above

2. In a transformer, the following winding has more cross-sectional area : 1
(A) Primary winding
(B) Secondary winding
(C) High voltage winding
(D) Low voltage winding

3. Cross-section of the iron core of a power transformer is approximately
circular. This is done because 1
(A) It is easy to assemble a circular core.
(B) It is easy to make a circular coil.
(C) Electromagnetic forces tend to make the coil circular.
(D) Of all of the above reasons

4. If the field circuit of a D.C. series motor gets opened on a small load then 1
(A) motor will pick up very high speed.
(B) motor will slow down.
(C) motor will stop.
(D) motor will run normally.

.311 3 P.T.O.

5. {XîQ> Ymam _erZ _| bmoh hm{Z`m± Bg_| CËnÞ hmoVr h¢ : 1

(A) `moH$ _|
(B) Ho$db Am_}Ma H$moa _|
(C) `moH$ Am¡a Am_}Ma _|
(D) Cn`w©ŠV _| go H$moB© Zht

6. Eogr hm{Z`m± Omo EH$ n[aUm{_Ì _| Zht hmoVr h¢ bo{H$Z Omo Ky_Zo dmbr {dÚwV² _erZm| _| hmoVr
h¢ : 1

(A) {hñQ>oao{gg Ed§ ES>r H$a§Q> hm{Z`m±
(B) Kf©U Ed§ dmB§S>oO hm{Z`m±
(C) Vm_« hm{Z`m±
(D) Mwå~H$s` hm{Z`m±

7. _moQ>a MbmVo g_` Cƒ Ymam H$m {Zdoe _w»` ê$n go {ZåZ Ho$ H$maU KQ>m`m OmVm h¡ : 1

(A) _moQ>a H$mo Vmnr` j{V go ~MmZo hoVw
(B) _moQ>a Ho$ amoQ>a H$mo ñQ>m{Q>ªJ PQ>Ho$ go ~MmZo hoVw
(C) bmBZ _| dmoëQ>Vm S´>m°n amoH$Zo Ho$ {bE
(D) Cn`w©ŠV _| go {H$gr Ho$ H$maU Zht

8. EH$ N>m{XV Y«wd _moQ>a _| `h Zht hmoVm h¡ 1

(A) H$å`yQ>oQ>a
(B) goÝQ´>râ`yJb pñdM
(C) g§Ym[aÌ
(D) Cn`w©ŠV g^r
.311 4

5. Iron losses in a D.C. machine take place in 1

(A) Yoke

(B) Armature core only

(C) Yoke and armature

(D) None of the above

6. Losses which do not occur in a transformer but do occur in rotating
electrical machines are 1

(A) hysteresis and eddy current losses

(B) friction and windage losses

(C) copper losses

(D) magnetic losses

7. In rush current to motor at starting is mainly reduced 1

(A) To save the motor from thermal damage

(B) To avoid starting shocks to the rotor of the motor

(C) To avoid voltage drop in the line

(D) Due to none of the above

8. A shaded pole motor does not possess 1

(A) Commutator

(B) Centrifugal switch

(C) Capacitor

(D) All of the above

.311 5 P.T.O.

9. _moQ>a dmB§qS>J Ho$ ObZo H$m H$maU {ZåZ hmoVm h¡ : 1

(A) g§Ym[aÌ Ho$ n[anW H$m Iwb OmZm
(B) g§Ym[aÌ Ho$ _mZ H$m ~Xb OmZm
(C) g§Ym[aÌ H$m$ bKw n[anW hmo OmZm
(D) Cn`w©ŠV _| go H$moB© Zht

10. EH$ Am§{eH$ Aíde{ŠV (FHP) H$s EH$-H$br` _moQ>a _| à`wŠV ñQ>m{Q>ªJ g§Ym[aÌ H$s Ym[aVm
{ZåZ Ho$ Amg-nmg hmoVr h¡ : 1

(A) 12 F

(B) 40 F

(C) 300 F

(D) 1000 F

11. 60% grgm Ed§ 40% {Q>Z Ho$ {_lYmVw H$mo H$hVo h¢ 1

(A) H$R>moa gmoëS>a
(B) _wbm`_ (Z_©) gmoëS>a
(C) ~«m±µO (H$m±gm)
(D) Cn`w©ŠV _| go H$moB© Zht

12. _wbm`_ (Z_©) gmoëS>a H$m JbZm§H$ {ZåZ hmo gH$Vm h¡ : 1

(A) 100 C go ZrMo

(B) 190 C Am¡a 250 C Ho$ ~rM

(C) 600 C
(D) Cn`w©ŠV _| go H$moB© Zht

.311 6

9. Burning out of motor winding is due to 1

(A) Open circuiting of capacitor

(B) Change in capacitor value

(C) Short circuited capacitor

(D) None of the above

10. Starting capacitor of a FHP single-phase motor will have a capacitance of
about 1

(A) 12 F

(B) 40 F

(C) 300 F

(D) 1000 F

11. An alloy of 60% lead and 40% tin is called 1
(A) Hard solder
(B) Soft solder
(C) Bronze
(D) None of the above

12. Melting point of a soft solder may be 1
(A) below 100 C
(B) between 190 C and 250 C
(C) 600 C
(D) None of the above

.311 7 P.T.O.

^mJ II
{H$Ýht nm±M àíZm| Ho$ CÎma Xr{OE & 25=10

13. dmoëQ>Vm Am¡a Ymam n[aUm{_Ìm| Ho$ {d{^Þ AZwà`moJ Š`m h¢ ? 2

14. EH$ n[aUm{_Ì {XîQ> Ymam na Š`m| H$m`© Zht H$a gH$Vm ? g§jon _| {b{IE & 2

15. {XîQ> Ymam _moQ>am| _| Am_}Ma à{V{H«$`m Š`m hmoVr h¡ ? 2

16. {XîQ> Ymam _moQ>am| _| Y«wdm| H$m Š`m H$m`© hmoVm h¡ ? 2

17. {XîQ> Ymam _moQ>a H$mo {~Zm ñQ>mQ>©a Ho$ Š`m| Zht MbmVo ? 2

18. N>m{XV Y«wd _moQ>a Ho$ {d{^Þ AZwà`moJ Š`m h¢ ? 2

19. gmoëS>[a¨J _| à`wŠV {d{^Þ VH$ZrH|$ Š`m h¢ ? 2

^mJ III
{H$Ýht nm±M àíZm| Ho$ CÎma Xr{OE & 35=15

20. EH$ H$moa Q>mBn n[aUm{_Ì H$s g§aMZm (~ZmdQ>) H$s ì`m»`m ñdÀN> {MÌ H$s ghm`Vm go
H$s{OE & 3

21. ñdÀN> {MÌ H$s ghm`Vm go µ\$sëS> H$ÝQ´>mob {d{Y Ûmam {XîQ> Ymam e§Q> _moQ>a H$s J{V {Z`§ÌU
{d{Y g_PmBE & 3

22. {XîQ> Ymam _moQ>am| _| à`wŠV VrZ-ßdm°BÝQ> ñQ>mQ>©a H$m n[anW {MÌ ~ZmH$a CgHo$ {d{^Þ A§J
Xem©BE & 3

23. [anëeZ ñQ>mQ>© _moQ>a Š`m hmoVr h¡ ? BgHo$ {d{^Þ AZwà`moJ Š`m h¢ ? 3

24. {Ì-H$br` àoaU _moQ>am| _| à`wŠV {d{^Þ ñQ>mQ>©am| Ho$ Zm_ {b{IE & CÝh| {H$VZr Aíd e{ŠV
H$s _moQ>am| _| à`wŠV H$a gH$Vo h¢ ? 3

25. {d{^Þ EH$-H$br` _moQ>am| Ho$ AZwà`moJ Š`m-Š`m hmoVo h¢ ? 3

26. EH$-H$br` _moQ>a _| CËnÞ hmoZo dmbo Xmofm| H$m nVm H¡$go bJmE±Jo ? H«$_dma {H«$`m{d{Y
{b{IE & 3

.311 8

PART II

Attempt any five questions. 25=10

13. What are the various applications of voltage and current transformers ? 2

14. Why can a transformer not work on D.C. ? Write in brief. 2

15. What is armature reaction in D.C. motors ? 2

16. What is the function of poles in D.C. motors ? 2

17. Why is a D.C. motor not started without a starter ? 2

18. What are the various applications of a shaded pole motor ? 2

19. What are the various techniques used for soldering ? 2

PART III

Attempt any five questions. 35=15

20. Explain the construction of a core type transformer with the help of a
neat sketch. 3

21. With the help of a neat sketch, explain the field control method of speed
control of D.C. shunt motor. 3

22. Draw circuit diagram of a 3-point starter used in D.C. motors and label
its parts. 3

23. What is a repulsion start motor ? What are its applications ? 3

24. Write the names of various starters used in 3-phase induction motors.
Which horse power motors are these used for ? 3

25. What are the various applications of different single-phase motors ? 3

26. How can faults in a single-phase motor be found ? Write the step-by-step
procedure ? 3

.311 9 P.T.O.

IÊS> I

{H$gr EH$ àíZ H$m CÎma Xr{OE & 51=5

27. `y{Zdg©b _moQ>a H$s g§aMZm (~ZmdQ>) H$m dU©Z BgH$m {MÌ ~ZmH$a H$s{OE & BgHo$
H$m`©H$mar {gÕm§V Ed§ Cn`moJ {b{IE & 5

28. gmoëS>[a¨J H$aZo Ho$ {d{^Þ VarHo$ Š`m h¢ ? gmoëS>a _| {d{^Þ YmVw H$m¡Z-H$m¡Z go h¢ Am¡a CZH$m
AZwnmV Š`m hmoVm h¡ ? 5

.311 10

SECTION B

Attempt any one question. 51=5

27. Describe with a sketch, the construction of a universal motor. Write its
working principle and uses. 5

28. What are the various methods of soldering ? What are the various
components of solder and their proportion ? 5

.311 11 P.T.O.