XII Class Assignment work physic

8/3/2019 XII Class Assignment work physic

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ACTIVITY NO. IAIM. In order to measure current though a resistor by measuring voltage across it,

a student draws the circuit diagram comprising a battery, resistor, rheostat, ammeter,

voltmeter and a one-way key as show in fig.

Apparatus

A battery, a resistor, an ammeter, a voltammeter, a rheostat, one-way key and connecting

wires.

Theory

To study current voltage relationship (To verify ohm’s Law)

The current voltage relationship can be studied by connecting a resistance

coil to a battery and measuring the current passing through it using an ammeter and

potential drop across it with the help of a voltammeter. The current in the circuit isvaried during the different observation with the help of the rheostat. The ratio of the

potential difference (V) across the resistance coil and the corresponding current (I)

flowing through it are measured for each observation. It will be found that

V/I= constant.

It, then shows that the current flowing through a conductor is directly

proportional to the potential drop across it.

I.e. it verifies ohm’s law.

Further for the variables V and I the equation represent a straight line. If a

graph is plotted between V (along X-axis) and I (along Y-axis), the graph will be a

straight line as shown in Fig. The straight line as shown in the fig. the straight line

graph between V and I shown that the current flowing through a conductor is

directly proportional to the potential drop across it.

Procedure.

1. Carefully look at the circuit diagram shown in Fig. reveals that the following

components have not been connected correctly.

a) A voltmeter is a high resistance instrument and is used to measure potential

difference across a resistor by connection it in parallel across the resistor. If the

voltmeter is connected as show in fig, practically no current will flow through the

resistor R.

b) An ammeter is a low resistance instrument and is used to measure current

through the circuit by connecting it in series to the resistor. If the ammeter is



connected as shown in fig, if at all any current flows through the circuit, the

ammeter will bypass the resistor and whole of the current will flow through.

c) For finding the resistance of a resistor, a rheostat is used for varying current in

the circuit. If the rheostat is used as in fig. it will offer a fixed value of resistance

in the circuit i.e. current in the circuit cannot be varied by using the rheostat as

such.

2. The correct circuit diagram for finding the resistance of a resistance by using an

ammeter and voltmeter is as shown in fig.

3. Disconnect the various components and connect them as shown in fig.

4. To find the value of the resistor R, note the reading of the ammeter (I) and voltmeter

(V). Apply the zero corrections (if any) to the observation ridings.

5. Repeat the experiment at least three times more.

6. Find the value of the resistor R by using the relations,

R=V/I

Precautions

1. An ammeter should always be connected in series for measuring current in the

circuit.

2. A voltmeter should be connected in parallel to the part of the circuit, across which

potential difference is to be measured.

3. So that a rheostat can be used to vary current in the circuit, its one base terminaland the top terminal should be used, while connecting it in the circuit.



ACTIVITY NO. 2 AIM: To use a Multimeter to:

a) Identify base of transistor.

b) Distinguish between n-p-n and p-n-p type transistors.

c)

See the unidirectional flow of current in case of a diode and an L.E.D.d) Check weather a given electronic components(e.g. Diode, transistor or IC is in

working order)

Apparatus

The given transistors, diode, LED, IC and a Multimeter.

Theory

Spherical Mirrors

The portion of a reflecting surface, which forms a part of a sphere, is called a spherical

mirror.

Consider a hollow glass sphere. If a portion of the hollow sphere is cut along a plane and

silvered, it serves as a spherical mirror.

1. Concave sphere mirror. A spherical mirror, who’s reflecting surface, is towards the

centre of the sphere, of which the mirror forms a part, is called concave spherical

mirror.2. Convex spherical mirror. A spherical mirror, who’s reflecting surface, is away from

the centre of the sphere of which the mirror forms a part, is called coves spherical

mirror.

Resistor

In electronic circuits, the resistor used is usually a carbon resistor.

A carbon resistor is a two terminal device and is made from a mixture of carbon

black, clay and resin. Two pieces of wire project out of the body of the resistor. The value of

a carbon resistor is marked on it according to a color code.

A resistor allows current through it both in D.C and A.C circuits. The value of a

carbon resistance offered by a resistor does change, when the polarity of the applied D.C.

Voltage is reversed. In other words, the magnitude of the current remains the same, when

the polarity of the applied D.C voltage is reversed across a resistor.

Capacitor



It is also a two terminal device.

a) Shows a paper or mica capacitor while shows a ceramic capacitor.

3. Junction Diode : It is a two terminal device and is represented by the symbol as

shown

The different junction diodes differ in their shapes and current ratings.

4.

Zener Diodes: Like a junction diode, it is also a two terminal device. It is representedby the symbol is as shown in.

5. Light Emitting Diode (L.E.D):

It is also two terminal devices.

(a) Represents a light emitting diode symbols. It has a transparent body. Its one end

face is flat, while the other is round in shape.

6. Transistor: A transistor is a three terminal device made from semiconducting

material, such as germanium and silicon. Three sections of transistors are called

emitter, base and collector.

7. Integrated Circuits: An integrated circuit consist of a silicon chip incorporating a

large number of microelectronic circuits. In other words, Integrated circuits consistsof whole systems rather than a seprate electronic components.

Procedure

1. By proceeding as in step 1 to 4 Activity no. 2, set the multimeter as an ohmmeter.

a) To identify the base of transistor:

2. Usually, the base lead of the transistor is between its emitter and collector leads.

However, in some transistors, it may not be so. In order to identify the base lead,

touch the two probes to the extreme two legs of the transistor. Note, weather the

resistance of the transistor between these two legs is low or high. Now interchangethe probes touching the two extreme legs of the transistor and again note, weather

the resistance of the transistor is low or high.

(i) In case resistance of the transistor is high in both the cases the central leg of

the transistor is base and the two extreme legs are emitter and collector. It is

because emitter collector junction offers high resistance in both the

direction.

(ii) In case resistance of the transistor is low in one direction and high in the

other direction, then one of the two extreme legs of the transistor is base.

3. In order to find out which of the two extreme legs in the base, call the two extreme

legs in the base, call the two extreme legs as the left and the right leg of the

transistor. Touch one of the two probes to the left leg and the other to the central

leg and note weather there resistance of the transistor between these two legs is

low or high. Now interchange the probes touching the left and central legs of the

transistor and again not, weather there resistance of the transistor is low or high.

(i) In case resistance of the transistor is high in both the cases, than the right leg

is the base of the transistor.



(ii) In case resistance of the transistor is low in one direction and high in other

direction, then the left leg is the base of the transistor.

(b) To find whether the given transistor is n-p-n or p-n-p:

4. Having indemnified the base of the transistor, touch the probe of black wire to the

base and the probe of red wire to any one of the other two legs. Note, whether the

resistance of the transistor is low or high.

(i) In case resistance of the transitory is high, it is a p-n-p transistor.

(ii) In case resistance of the transistor is low, it is an n-p-n transistor.

(c) To see unidirectional flow of current feature in a junction diode and L.E.D.:

5. By proceedings as in steps in 1 to 4 of Activity no. set the Multimeter as an ohm

meter.

For Junction diode:

6. Touch the two probes of the Multimeter to the two end terminals of the junction’s

diode and note whether the resistance of the junction diode is low or high. Now,

interchange the tow probes and again note whether the resistance of the junction

diode is low or high.

For L.E.D.:

7. By proceeding as in step, repeat the observation for the L.E.D.

It will be found that if the resistance of the L.E.D is high in the first case, it will be low

in second case and vice-versa. Further, the L.E.D will glow by emitting light, when its

resistance is low. It shows the unidirectional flow of current in an L.E.D.

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XII Class Assignment work physic