Revision Exercise 2nd Term 2014

7/26/2019 Revision Exercise 2nd Term 2014

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SECOND TERM PHYSICS REVISION EXERCISE

TOPIC : ELECTRISTATICS

1. (a) Q1= + 40 C 40cm Q= +!" C

!0 cm #0 cm

$%&' II

Q!= * "0 C

Figure II shows three point charges + 40 C, +36 C and -60 C are fixed at corners of a

Right-angled triangle. eter!ine the magnitudeand directionof the ',-a- ,c-%c

/cacts on charge "#$% the other two charges ( #)


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(c) (i) Write an expression which shows the relationship between electric field, E and

electrical potential, V? (1)

222222222222222222222222222222222222222

(b)

V(Volt)

15

X (m)

-8 -6 - ! 5 "

-#5

$efer to the % & ' raph abo%e, setch a raph to show the %ariation of E with ' ? (4)

4. D

40 cm

A C

30 cm B 30 cm

- 80

C +45

C

*i+re


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$efer to fi+re , point chare 1 - 8! . # +/5 . are placed at point 0

and . respecti%el2 03 3. ! cm, and 34 /! cm2 4etermine

(a) the electrical potentialat point 3 and 4 ? (3)

-

(b)Work doneto brin a chare of 65 . from point 4 to 3 ? (2)

777777777777777777777777777777777777772

(c ) 4etermine the res+ltant electric field acts on point 3

. (a) tate !a"##$# la%& (1)

(b) 9se :a+ss;s law to derive the electric field strength, Ethat is prod+ced

b a chared sphere with radi+s, $ as shown below (5)

+ +

+ +

+ + C'ared #p'ere

+ +

+ +

$efer to o+r e'pression of E, sketcha raph to show the variation of E

with distance, r . (3)


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(c)

30o

0.5

0 small neati%e chared sphere with of mass 0.5 hans from a liht strin in an

electric field of intensit 800 *C-1prod+ced b a chared plate2


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E= 20.0 V, r = 1.0

R= 6.0

R1= 4.0

E2 , r2=1.0

R2= 1.0

E1 , r1= 1.0

I= 1.0 A

I2=2.0 A

I1

a

b

c d

e

fX

Y

777777777777777777777777777777777777777

#2

A5 : (6) (%) 17V8 9V (%%) 1!V8 *1!V8 !V (b)


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7.2 V

E

R

0.96 A

I

0.40 A

Determine

(a) t'e c"rrent , %'ic' lo%# t'ro"' t'e 10.0

resistor,

() e.m.

(c ) re#i#tance .

67,C CA7AC,6

12

.1 # 9

. 1# 9

.# / 9


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20V d.c

2.0 !

0." !#.6 !

6 V

>hree capacitors are connected as shown in the abo%e fi+re2 4etermine

(a) the e+i%alent capacitance?

(b) the potential difference across 1# * capacitor?

(c ) the chare stored in each capacitor?

#2 (a) >hree initiall +nchared capacitors of capacitance #2! *, !25* and 26 *are connected to s #! V batter as shown in the fi+re below2

4etermine


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(i) the effecti%e capacitance

(ii) the total chare s+pplied b the batter

(iii) the chare on the 26 * capacitor

(i%) the chare on the #2! * and on the !25 * capacitor

2 (a) 4efine capacitanceof a capacitor? (1)

(b) :plainwhat is the effect on electric field of a parallel plate capacitor when adielectricis inserted between the two plates of the capacitor2 ()

/tate al#othe effect of dielectric on the potential difffrence, V between the twoplates and the %al+e of the capacitance2 (#)

(c) (i) 4efine time constant, for charin circ+it of capacitor2 (1)

(ii) >he diaram below shows a circ+it +sed to chare a capacitor, . thro+h a hih

resistance $2

$ .


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witch

e2m2f2 E

3 considerin the charin c+rrent, showthat the potential difference across

the capacitor at time t after the switch is closed is i%en b e+ation below

; < ( 1 = e

= t > C

) (4)

(d) etch a raph to show the %ariation of aainst t and %ariation of < aainst t

for two different re#i#tor o re#i#tance 1 and 2%'ere 1 ? 2 (4)

/2

5 @

Voltmeter

/ V 8 * ;


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Aetalball witch

3at

>he fi+re shows a metal ball was held away from the batwhile closing the switch Sforsome instant +ntil the capacitor was fully charged

(a) (i) Drawa raph to show the variation of potential difference across thecapacitor with time?

V (Volt)

t( s)

-

(ii) Determine the initial currentflows in the circ+it at the moment the switch Sis closed?

(iii) 4etermine the time takenfor the capacitor to achie%e p.d. o 3 ;?

(b) 0fter the capacitor is f+ll chared, the switch is then opened and the metal ball isreleased toward the bat

(c)(i) Explainwhat will happen to the capacitorafter the metal ball maes


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contact with the bat?

77777777777777777777777777777777777

777777777777777777777777777777777772

777777777777777777777777777777777777772

(ii) Drawa raph to show the variation of potential difference across the capacitor with time?

V (%olt)

t (s )

(iii) Calculate the time contactbetween the metal ball and the bat if the %oltmeter showin a readin of 12! V before the metal ball is bo+nded

bac?

52

1!2!V

#!!* 6!2!@

S

&o C.R.'


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!2! @

>he abo%e circ+it shows circ+it with witch and a capacitor of capacitance #!! * whichma be chared b a batter of e2m2f2 1!2! V and neliible internal resistance connected

in series with a resistor of resistance !2! @, >he switch also enables the capacitor to

be dischare thro+h a resistor of resistance 6!2! @2 >he p2d2 V across the capacitor is

monitored +sin a s+itable cathode-ra oscilloscope (.2$2B2) to infinite resistance2

(a) (i) 4etermine the time constant for the charin of the capacitor?

(ii) 4etermine the time constant for the discharin of the capacitor?

(b) >he capacitor, initiall +nchared, is connected to the batter for time of 52! s andthen di#c'ared a "rt'er period o 5.0 # 2 At t < 10.0 # t'e capacitor i#aain c'ared or anot'er period o 5.0 #.

(i) 4etermine the p.d. acro## t'e capacitor at t < 5.0 # t < 10.0#and

t < 15.0 #.?

(ii) /ketc' on the same a'es, the appearance of the trace on the .2$2B or t'e15-#econd period&

;(olt)


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0 5 10 15 t (#)

TOPIC : ELECTRIC C3RRENT

1(a) erive an expressionof the c"rrent ,in a piece of wire in termsof the cro##

#ectional area A, the drit elocit ;, the electron c'are eand the n"mer

o ree electron per "nit ol"me n&

2 (b) efinec"rrent den#it, @and then write down an expressionthat relates

c"rrent den#it @ to electrical cond"ctiit

and electrical ield

(c)!rite an expressionthat relates the drit elocit ;to electrical ield and

t'e mean time et%een colli#ion. ence ded"ce a orm"la or t'e

electrical cond"ctiit

in term# o n e

and t'e electron ma## m a#

ien elo%

< ne2

m

Explain the effect on electrical conductivit"of the metaland semiconductor

when the temperat+res of the materials increase?

67,C A!*,C 9,D

1 X

C cm


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1!0

1#cm 50

$

= # cm

>he diaram shows a c+rrent of 1! 0 in a lon straiht %ertical wire X= and c+rrent of

50 flows in a rectan+lar coil C$2 >he coil has #! t+rn and dimensions C cm

and C 1# cm2 >he side C is placed parallel to X= and at a distance of # cm

from X=2

(a) 4etermine the manit+de and direction of the manetic force that acts on

(i ) wire C

(ii ) wire $

(b) E'plain whether the coil will rotate abo+t an a'is ?

777777777777777777777777777777777777777

7777777777777777777777777777777777777777

77777777777777777777777777777777777777722


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7777777777777777777777777777777777777772

2E E E E E E E E E

X X X ; X X X X X X

X X X X X X X X X

X X X X X X X X X

X X X X X X X X X

X X X X X X X X X

>he abo%e diaram shows an electron mo%es with a +niform %elocit V which is

perpendic+lar to the manetic field in a %ac++m2 >he mo%in path of the electron is a circle

orbital of radi+s #2! miff the manetic fl+' densit is 52! ' 1!

-

> and its direction is pointinto the pageand the specific chare eDm of an electron is 12"6 ' 1!11.D2

(a) 4etermine(i) linear %elocit and an+lar %elocit of the electron2

(ii) period of orbit

(b) etch the mo%in path of the electron in the manetic field2(c) etch the direction of electric field E alon the mo%in path of the electron which

Will mae the electron mo%es in a straiht line

C2 >he fi+re shows a wire frame in the form of trianle

C$ carrin a c+rrent of 25 0 inside an +niform "!o

manetic field of fl+' densit 825 >2 3(i)4etermine the manit+de and direction of the manetic force acts on the sides 6!o 5!o

(a) C (b) C$ (c) $ $

(


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J

KL

M

I

/2

he rod isfree to slide on the metal strips 03 and .42 0n +niform manetic field of fl+' densit

!26 > acts %erticall downwards and the %al+e of c+rrent flows into the rod is 825 0

(a) abel the entire forces act on the rod2

(b) .alc+late the res+ltant force acts on the rod2

(c) 4etermine the acceleration of the rod and itsdirection of mo%ement?


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52 *i+re shows three parallel lon straiht riid wires

X, = and F carr the c+rrent of 1!0, 150 and #!02respecti%el 1!0 150 #!0

(a) 4etermine the res+ltant manetic field actson point C of wire = d+e to wire X and F? X = F

(b) 4etermine the force act on wire =

. 7

CA7 C6A!*,C ,*DFC,6*

1. (a) /tate t'e laws of electromagnetic induction& rod E E E E E

(9arada$# la% and enG$# la%) E E E E E() F#e t'e diaram ien elo% ded"ce E E E E E t'e expression of induced e.m.f, Ein term# E E E E E o manetic ield B lent' o t'e cond"ctor E E E E E and elocit o t'e cond"ctor ; & E E E E E (eer pae 8 H ) manetic ieldB

(c ) F#e t'e diaram ien elo%. derive an expression of induced e.m.f


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, Ein t'e plane coil %it' * t"rn# and area A %'en it i# rotated in t'e "niorm manetic ield B a# elo%

< *BAW #in %t #ketch a graph E against t to #'o% t'e ariation o %it' t&

(eer pae 10 )

2. (a) /tate t'e meanin o I#el- ind"ctionJ and Im"t"al ind"ction I& ()

B "#in t'e principle# o #el-ind"ction and m"t"al ind"ction .eer tot'e aoe diaram derie an e:pre##ion o m"t"al ind"ctance a#

elo% < *1*2r2

67,C AC*A,*! CF*

1 0n ind+ctor with ind+ctance #5! mG is connected to a 02. s+ppl with pea

Voltae /! V and fre+enc 5! GH2 4etermine

(i) reactance of the ind+ctor


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(ii) root mean s+are (r2m2s2) of the c+rrent flows in the ind+ctor

#2 0n alternatin %oltae V is represented b the followin e'pression

; < 230 /in 500t


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(d) 4eri%e the e$uation representing instaneous powerin the capacitor and then

.alc+late the maximum instantaneouspo%erfor the capacitor?

1!2 (a) >he diaram below shows a 02. 2circ+it consists of a p+re ind+ctor of ind+ctance 2

, < ,o/in Wt

7"re ,nd"ctor

02.

witch

(a) +ppose the alternatin c+rrent, < flows in the circ+it at time t as the switch closed

is i%en b e+ationI , < ,o/in Wt

educethe e$uation of potential difference, %across the ind+ctor at time t when


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the switch is closed2

(b) etch a raph of ( i) , aain#t t and (ii) ; aain#t t on the #ame a:i#and then

describe thephase differencebetween < and V?

(c) 4efine reactanceof t'e inductorand then ded+ce an e+ation of reactance E of

the ind+ctor in terms of fre$uenc", f and inductance, L.

(d ) 0n ind+ctor with ind+ctance #5! mG is connected to a 02. s+ppl with pea

Voltae /! V and fre+enc 5! GH2 4etermine

(i) reactance of the ind+ctor

(ii) root mean s+are (r2m2s2) of the c+rrent flows in the ind+ctor

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Revision Exercise 2nd Term 2014