Section B Activities

7/26/2019 Section B Activities

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C.C.H.S. MANSAROVAR

CLASS-XII PHYSICS Section A and B Practical ActivitiesSECION- B B-! ACIVIY N"MER######. $AE######

AIM % To study effect of intensity of light ( by varying distance of the source ) on an L.D.R.

A&&arat's- An L.D.R.(light dependent resistor), a metre bridge, a resistance box, a galvanometer, oc!ey, Leclanche

cell"battery, connecting #ires.

$ia(ra)-

*eor+

A light dependent resistance (L.D.R.) consists of consists of cadmium sulphide. $ts resistance depends upon the

intensity of light varies from about % &' in complete dar!ness to about % ' in daylight.

The un!no#n resistance of L.D.R., using the meter bridge, is given by x * R (100−l)

l ++..(%) , #here R is

resistance from the resistance box and l is position of null point or balance point.

Proced're

%. et up slide #ire bridge circuit #ith L.D.R. as un!no#n resistance as sho#n in -igure.

. /lace a bulb at a height of about %0 cm, from L.D.R. 1xpose the L.D.R. to light for about minutes. Ta!e out

suitable resistance R from the resistance box and find the position of null point. 2alculate resistance of L.D.R. using

e3uation (%).

4. Repeat the step by changing the height of bulb to % cm, 5 cm, 6 cm and 4 cm. 2alculate the resistance of L.D.R.

each time.

l.7o

.

8eight of the bulb

from L.D.R. (cm)

Resistance (ohm) /osition of null point l

(cm) x * R (100−l )

l

(ohm)

%.

.

4.

9.

0.

Conclsion,Res'lt

-ron the observation table, it is clear that as the distance of the bulb from L.D.R. decreases or intensity of light fallingon L.D.R. increases, the resistance of L.D.R. also decreases.

Preca'tions

%. The value of R should be chosen suitably such that balance point or null point lies near the middle of the #ire.

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CLASS-XII PHYSICS Section A and B Practical Activities. The plugs of the resistance box should be made tight by giving them t#ists.

4. Distance of the filament of the bulb from L.D.R. should be measured accurately.

SECION- B B- ACIVIY N"MER######. $AE######

AIM % To identify a diode, a L1D, a transistor, and $2, a resistor and a capacitor from mixed collection of such items.

A&&arat's- Diode, L1D, transistor, $2 (integrated circuit), resistor, capacitor and multimeter.

$ia(ra)-

*eor+

-rom the given collection of diode, L1D, transistor, $2, resistor and capacitor, these devices can be identified on the

basis of their appearance and #or!ing.

i/ An inte(rated circ'it IC/ 0 $t is in the form of a rectangular or circular chip #ith flat bac! and is a multiterminal

device. :enerally, it has eight, sixteen or more pins.

ii/ ransistor 0 A transistor is a three terminal device.

iii/ $iode 0 A diode is a t#o terminal device. $t conducts #hen for#ard biased and does not conduct #hen reverse

biased.

iv/ Li(*t e)ittin( diode I1E$/ 0 A L1D is a t#o terminal device. $t conducts #hile for#ard biased and does not2onduct #hen reverse biased. $t emits light #hile conducting.

v/ Ca&acitor 0 $t is also a t#o terminal device. ;hen a capacitor is charged or discharged through a resistor, current

decays exponentially #ith time in both cases (charging as #ell as discharging). -urther, a capacitor conducts a.c. and

does not conduct d.c.

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C.C.H.S. MANSAROVAR

CLASS-XII PHYSICS Section A and B Practical Activitiesvi/ Resistor 0 A resistor is a t#o terminal device. $t conducts either for#ard biased or reverse biased. ;hen a d.c.

voltage is applied across it, current through it remains steady or constant. $t conducts both d.c. and a.c.

Proced're

%. An integrated circuit ($2) and a transistor can be identified ust by appearance. $f the component has large number

of pins or legs and is in the form of chip, then it is $2. $f the component has three terminals or legs, then it is a

transistor.. The components having t#o legs or terminals may be diode, L1D, capacitor or resistor. These components can be

distinguished from one another by using a multimeter as an ohms<meter as explained belo# =

(a) $nsert the blac! and red leads (or probes) into the common and positive terminals of the multimeter and turn the

selector s#itch to &' position for chec!ing the continuity.

(b) Touch the probes to the t#o ends of each component and observer the deflection on resistance scale of the

multimeter. 7o#, interchange the position of the t#o probes and again note the deflection.

(i) $f deflection is observed in one case and >ero deflection in the other case, then the component is diode.

(ii) $f deflection is observed in one case along#ith emmission of light and no deflection is observed in the other case.

tlren component is LE$.

(iii) $f large deflection is observed #hich then gradually decreases to >ero, then component is capacitor.

(iv) $f the same constant deflection is observed in the t#o cases, before and after interchanging the probes, then the

component is resistor.

O2servations

l.7o

.

7umber of legs"pins Device

%. 1ight or more $.2.

. Three Transistor

4. T#o Diode, L1D, 2apacitor, Resistor

l.7o

.

-lo# of current Device

9. ?nidirectional, but no light is emitted Diode0. ?nidirectional, light is also emitted L1D

6. 2urrent decays to >ero gradually or suddenly 2apacitor

@. teady current, both before and after

interchanging probes

Resistor

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C.C.H.S. MANSAROVAR

CLASS-XII PHYSICS Section A and B Practical Activities

SECION- B B-3 ACIVIY N"MER######. $AE######

AIM % ?se of multimeter to (i) identify base of transistor, (ii) distinguish bet#een n<p<n and p<n<p type transistor

(iii) see the unidirectional flo# of current in case of diode and an L1D, (iv) 2hec! #hether a given electronic

component (e.g. diode, transistors, or $2) is in #or!ing order.

A&&arat's- Diode, L1D, n<p<n transistor, p<n<p transistor, $2 (integrated circuit), a multimeter.

Proced're

i/ Identi4ication o4 2ase o4 a transistor 0 The multimeter is used as an ohm<meter by turning the selector the selector

s#itch to either &' or ' range. The blac! or common lead is ta!en as positive because positive of the multimeter

battery is connected to this common terminal.

a/ 5irst )et*od 0 The probes of the multimeter are touched #ith t#o legs of the transistor and then position of the

probes are interchanged. $f the multimeter sho#s no deflection in both the cases then the third leg is base. These t#o

legs used are collector and emitter since emitter<base unction offers high resistance in both the cases.

2/ Second )et*od 0 2onnect one probe of the multimeter to a particular leg of the transistor. Touch the other probe#ith the remaining t#o legs in turn. $f multimeter sho#s deflection in both cases, then the first leg is base.

ii/ Identi4ication o4 n-&-n or &-n-& transistor 0 Bnce, the base has been identified, then=

(a) 2onnect probe of the blac! lead to the base and probe of the red lead to the either of the remaining legs. $f

multimeter sho#s deflection, the given transistor is n<p<n transistor.

(b) 2onnect probe of the red lead to the base and probe of the blac! lead to the either of the remaining legs. $f

multimeter sho#s deflection, the given transistor is p<n<p transistor.

iii/ "nidirectional 4lo6 o4 c'rrent in diode,LE$ 0 The probes of multimeter are touched #ith the t#o ends of

diode"L1D and then connections are interchanged. $f multimeters sho#s deflection in one case only, the given

component (diode"L1D) sho#s unidirectional flo# of current.

iv/ o c*ec7 '& 6*et*er a transistor is in 6or7in( order or s&oiled 0 The probes of the multimeter are touched

#ith the t#o ends of the diode and then connections are interchanged.(a) $f multimeter sho#s deflection in one case and no deflection in other case, then diode is in #or!ing order.

(b) $f multimeter sho#s deflection in both cases, then the diode is spoiled.

v/ o c*ec7 '& 6*et*er a transistor is in 6or7in( order or s&oiled 0 elect t#o legs of transistor bet#een #hich

there is conduction in for#ard biasing or reverse biasing, these legs #ill be collector and emitter. $f this is not the case,

then transistor is spoiled. ?sing third terminal as base, apply for#ard bias and reverse bias bet#een 1C and 2C

unctions, if there is conduction in across both the unctions during for#ard bias and no conduction during reverse

bias, then transistor is in #or!ing order, other#ise it is damaged.

vi/ o c*ec7 '& 6*et*er on IC is in 6or7in( order or s&oiled 0 Loo! at the number mar!ed on the $2 and chec! up

the functioning of various gates according to specifications given in the manual.

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C.C.H.S. MANSAROVAR

CLASS-XII PHYSICS Section A and B Practical ActivitiesSECION- B B-8 ACIVIY N"MER######. $AE######

AIM % To observe refraction and lateral deviation of a beam of light incident obli3uely on a glass slab.

A&&arat's- A glass slab, a sheet of #hite paper, dra#ing board, all<pins, cello tape or dra#ing pins, ruler, pencil, etc.

$ia(ra)-

*eor+

#hen a ray of light is incident from air on to a glass slab, it suffers refraction from rarer to denser medium. Therefore,

it bends to#ards the normal such that angle of refraction r is less than angle of incident i. The ray 1- suffers refraction

at the opposite face of the glass slab and goes from denser to rarer medium. Therefore, it bends a#ay from the normal.

$t emerges out along -: and is !no#n as emergent ray. -rom the -ig, it is clear that =

(i) the emergent ray is parallel to the incident ray, and

(ii) the emergent ray is laterally displaced from the incident ray by distance d, the lateral displacement is given by

d * t sin

(i−r )cosr , #here t is the breadth of the glass slab.

Proced're

%. -ix a sheet of #hite paper on the dra#ing board using cello tape or dra#ing pins. /lace a glass slab on this #hite

sheet of paper and mar! its boundary #ith a sharp pencil.

. Remove the glass slab and mar! the incident ray /1 and normal &&" as sho#n in figure. Replace theglass slab.-ix

t#o all<pins / and vertically on the incident ray and loo! for their image from the opposite side.

4. -ix t#o more all<pins R and vertically such that the tips of these pins R and and images of tips of pins / and

all are in same straight line.

9. Remove the glass slab. Eoin R and and extend it further so as to meet the boundary 2D at point -. Eoin 1-. Then,

1- is the refracted ray. 1xtend the incident ray further by dotted line as sho#n in -ig. $t is observed that emergent ray

is parallel for the incident ray but laterally displace from it.

0. Repeat the experiment by putting the glass slab breadth #ise. $t is found that emergent ray is again parallel to theincident ray but lateral displacement is proportional to the thic!ness t of the glass slab traversed by light.

Concl'sion , Res'lt

l. The emergent ray is parallel to the incident ray but it is displaced laterally.

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C.C.H.S. MANSAROVAR

CLASS-XII PHYSICS Section A and B Practical Activities. The lateral displacement of the emergent ray increases #ith the increase in thic!ness of glass traversed by light.

SECION- B B-9 ACIVIY N"MER######. $AE######

AIM % To observe diffraction of light due to a thin slit.

A&&arat's- An optical bench #ith t#o uprights. t#o ra>or blades fixed on a glass plate #ith their sharp edges exactly

parallel to each other, a blac! paper, a pencil laser and a screen.

*eor+

;hen a parallel beam of monochromatic light is passed through a narro# slit, it bends around the corners of the slit

giving rise to the phenomenon of diffraction. The pattern obtained on the screen consists of central maxima having

large intensity surrounded by alternate minima and secondary maxima of rapidly decreasing intensity (-ig.). The

condition for formation of minima and secondary maxima are

d sin F * nG (&inima) and d sin F * (n H %) λ

2 (&axima)

Proced're

% . ;ith the help of cello<tape, fix t#o ra>or blades #ith their sharp edges parallel and extremely close to each other so

that a narro# rectangular slit is formed bet#een the sharp edges.

. 2over the glass plate, leaving the rectangular slit uncovered, #ith blac! paper.

4. 8old the glass plate in a lens or mirror holder on an optical bench and pencil laser on another holder at a distance of

about cm from the slit.

9. Bbserve the light coming out of the slit on a #all"screen at a distance of about m from the slit.

0. $t is found that the pattern on the screen"#all consists of broad central maxima flan!ed on both sides by alternate

minima and secondary maxima of decreasing intensity.

Concl'sion,Res'lt

A diffraction pattern consisting of a large number of bright and dar! fringes parallel to the slit is observed on thescreen.

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C.C.H.S. MANSAROVAR


SECION- B B-: ACIVIY N"MER######. $AE######

AIM % To obtain a lens combination #ith the specified focal length by using t#o lenses from the given set of lenses.

A&&arat's- An optical bench, a large number of different focal lengths, a lens holder can hold t#o lenses touchingeach other, three uprights.

*eor+

The focal length (f) of t#o thin lenses of focal lengths f % , and f placed in contact #ith each other is given by

1

f *

1

f 1

+1

f 2

The po#er of the combined system is given by / * /% H / , #here /% *1

f 1

and / *1

f 2

are po#ers of the

individual lenses.

Let #e #ant to obtain a lens system of focal length l cm from a given set of lenses in #hich one lens is of focal

length 4 cm. The focal length of second lens should be 1f 2

* 1 F

< 1f 1

* 110

< 130

=3−130

* 115

*I f * %0 cm

Proced're

%. -ind the rough or approximate focal length of various lenses by obtaining sharp and clear image of distant obects

on the screen or #all and select the convex lens of focal length of %0 cm.

. /ut the given lens of focal length 4 cm and the lens of focal length %0 cm in contact #ith each other. The

combination #ill be e3uivalent to a convex lens of focal length % cm.

4. ?sing optical bench method, it is found that the image of an obect placed at - * cm distance is formed at

distance - * cm or the other side of the lens. Thus, the combination has a focal length of % cm.

Preca'tions

l. The t#o lenses should be thin lenses.

. The t#o lenses should have the same aperture.

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C.C.H.S. MANSAROVAR


a

pg. 10

Section B Activities

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