Experiment: Determining High Resistance using Neon Flash Lamp &
Capacitor
Apparatus: Resistor of unknown resistance, Diode, Power Supply, Neon Flash Lamp apparatus,
Stop watch, Connecting Wires.
Circuit Diagram
Procedure:
1.
2.
3.
4.
First of all, set the resistance at 1 MΩ.
Switched on the power supply and record the average time for 20 flashes.
Repeat the time recording process to get multiple values.
Plot a graph between “R” and “T”.
Formula for finding the time period of a capacitor:
Time Period = (Time for 20 flashes) / 20
T = t / 20
Observations and Calculations:
No.of obs
Known
resistance
R (M)
Time for 20 flashes
t1
t2
𝒕=
Time period
T=t/20 (sec)
(𝒕𝟏 + 𝒕𝟐 )
𝟐
Experiment: Finding the resistance of Galvanometer by Half
Deflection method
Apparatus: Galvanometer, High Resistance Box (HRB), Low Resistance Box (LRB), Battery,
one-way keys, connecting wires and sand paper.
Circuit Diagram
Procedure:
1. Clean
the
connecting
wires
with
sand
paper
and
make
neat
and
tight connections as per the circuit diagram
2. From the high resistance box (1-10 kΩ), remove 5kΩ key and then close the key K1. Adjust
the resistance R from this resistance box to get full scale deflection on the galvanometer
dial. Record the values of resistance, R and deflection 𝜽.
3. Insert the key K2 and keep R fixed. Adjust the value of shunt resistance S to get the
deflection in the galvanometer which is exactly half of θ. Note down S. Remove plug K2
after noting down the value of shunt resistance, S.
4. Take five sets of observations by repeating steps 2 and 3 so that θ is even number of
𝜽
divisions and record the observations for R, S, 𝜽 and 2 in tabular form.
5. Calculate the galvanometer resistance G and figure of merit k of galvanometer using
formula given in the below table.
Precautions:
1. Key K1 should be closed only after taking some high resistance.
2. The deflection should be in even number of scale.
3. Zero error of the galvanometer should either be removed or accounted for
Observation and calculation:
No.
of
Obs
Resistance Deflection
R
𝜽
Shunt
Half Deflection
resistance
𝜽
𝟐
S
𝑮=
𝑹×𝑺
𝑹−𝑺
𝜿=
𝑬
𝟏
∙
𝑹+𝑮 𝜽
Experiment: Study of the variation of electric current with intensity
of light using a photocell
Apparatus:
Photo-electric
cell,
sensitive
galvanometer,
battery,
rheostat,
key,
electric
bulb
Circuit Diagram
Procedure:
1. Arrange the apparatus as shown in the figure. Here all the components are in
series. The bulb should be selected and fixed in such a way that its point light
falls on the photo-electric cell.
2. Keep the source as close as possible to the photocell
3. Using white light as source determine the stopping potential (i.e. the negative anode
potential where the current becomes zero)
4. Now without changing the distance between the source and the photocell, insert a filter
(say green) of known wavelength in the path of the light (in the slit provided)
5. Put on the lamp. Adjust the suitable deflection in the galvanometer.
6. Note
the
deflection,
θ
in
the
galvanometer
(or
micro-ammeter)
and
the
corresponding distance, d of the photo-cell from the lamp. Change the distance d
in regular steps and note the deflection θ in the galvanometer.
7. Repeat the step 4 and 5 or other filters also
8. Draw a graph between 1 / d2 verses θ. It will be a straight line.
Precautions:
1.
The voltage of the bulb must remain constant.
2.
A point source of light should be used.
3.
Start the experiment from maximum distance and decrease to minimum.
Observation and calculation:
No.
Filter
of
Wavelength
Current
Stopping
𝝀
I
Potential
Obs
V
Color
× 𝟏𝟎−𝟏𝟎 m
𝝁𝑨
Red
Yellow
Green
Violet
Velocity of light = c = 𝟑 × 𝟏𝟎𝟖 𝒎𝒔−𝟏 m
Charge on an electron = e = 1.6 x 𝟏𝟎−𝟏𝟗 coulombs
Mean calculated value of h = ---------- × 𝟏𝟎−𝟑𝟒 J-s
Standard value of h = 6.626 × 𝟏𝟎−𝟑𝟒 J-s
volts
𝒉
=
𝒆(𝑽𝟏 − 𝑽𝟐 )𝝀𝟏 𝝀𝟐
𝒄(𝝀𝟐 − 𝝀𝟏 )
J-s
Experiment: Conversion of galvanometer (of known resistance and
figure of merit) into an ammeter of a desired range (say 0 to 30 mA)
a voltmeter of desired range (say 0 to 3 V) and to verify the same.
Apparatus:
A galvanometer of known resistance and figure of merit, a constantan or manganin wire of 26 or
30 SWG, a battery or a battery eliminator, one way key, a rheostat of range 200 Ω, an ammeter of
0-30 mA range, a voltmeter of 3 V range, connecting wires and sand paper.
Circuit Diagram
Procedure:
1. Determine the galvanometer resistance G and figure of merit k as per the procedure given
in experiment of half deflection method.
2. Count the total number of divisions N on either side of zero of the galvanometer scale.
3. Calculate the current Ig for full scale deflection in the galvanometer by using the relation
Ig= Nk, where k is the figure of merit of the galvanometer.
4. Calculate the shunt resistance S using the formula 𝑆 = 𝐼
𝐼𝑔 𝐺
0 −𝐼𝑔
5. Measure the radius r of the wire and from the given value of the specific resistance ρ,
calculate the length of the wire l, for resistance S [use the formula 𝜄 =
𝑆𝜋𝑟 2
𝜌
]
6. Let the calculated length of the wire be 10 cm. Then cut 3-4 cm extra and put it in parallel
to the galvanometer and complete the circuit as shown in circuit diagram.
7. Adjust the length of the wire so that when we see full scale deflection in the galvanometer,
the current in the ammeter is 30 mA.
8. Thus the galvanometer is now converted to an ammeter whose range is 30 mA.
9. Now measure the exact length of the shunt wire and calculate its resistance by using the
previously measured value of radius and the known value of specific resistance.
𝜄×𝜌
10. Compare the above value of resistance to the one calculated using the formula 𝑆 ′ = 𝜋𝑟 2
Precautions:
1. Use the ammeter for verification which has the same range as the range of conversion.
2. Cut about 3 to 4 cm extra to the calculated length of the wire.
3. After adjusting the length of the wire, measure the length of the wire between the two plugs
carefully.
Observation and Calculation:
No.of
Galvanometer
Figure of
Obs
resistance
merit
G (ohm)
𝒌 (ampere
/ division)
𝑰𝒈 = 𝑵𝒌
(ampere)
Mean
Radius
observed
R=D/2
diameter
(cm)
D (cm)
𝑺′ =
𝜾×𝝆
𝝅𝒓𝟐
Experiment: Conversion of galvanometer (of known resistance and
figure of merit) a voltmeter of desired range (say 0 to 3 V) and to
verify the same.
Apparatus:
A galvanometer of known resistance and figure of merit, a constantan or manganin wire of 26 or
30 SWG, a battery or a battery eliminator, one way key, a rheostat of range 200 Ω, an ammeter of
0-30 mA range, a voltmeter of 3 V range, connecting wires and sand paper.
Circuit Diagram
Procedure:
1. Calculate the value of the series resistance R for given values of V0, Ig and G.
2. Make the connections as shown in circuit diagram by connecting a cell and converted
galvanometer and the voltmeter of nearly the same range in parallel, with a high resistance
rheostat Rh.
3. Close the key K and adjust the rheostat so that the voltage shown in the voltmeter is equal
to the desired range (say 3 V). Simultaneously, adjust the position of the slider of the
rheostat and also the resistance from the resistance box so that when full scale deflection
is observed on the galvanometer, the voltmeter shows 3 V.
Observation and Calculation:
No.of
Galvanometer
Figure of
Obs
resistance
merit
G (ohm)
𝒌 (ampere
/ division)
N
𝑰𝒈 = 𝑵𝒌
Total
resistance
(divisions)
(ampere)
taken out
from the
resistance
box (ohm)
Radius
𝑹
=
𝑽𝟎
−𝑮
𝑰𝒈
(ohm)
Experiment: RLC Circuit
Apparatus:
Function generator, inductance coil (1mH), capacitors (0.01µF), three resistances, Cathode Ray
Oscilloscope (CRO), breadboard etc.
Circuit Diagram
Bandwidth of series LCR resonance
circuit
Procedure:
1. The series LCR circuit is to be connected as shown in circuit diagram.
2. Set the inductance and the capacitance to low values (L ∼ 1mH, C ∼ 0.01µF), such that
1
the resonant frequency 𝑓0 = 2𝜋√𝐿𝐶 is the order of few kHz.
3. Vary the frequency of the oscillator and record the voltage across the resistance R.
4. Repeat it for three values of the resistors (say R = 56Ω, 100Ω and 470Ω).
5. Take data of about 25 points for each resistance and plot the current amplitude as a function
of frequency f.
6. Find the experimental resonance frequency 𝑓0′ from plot.
Observation and Calculation:
No of Frequency
obs
I= V/R
(HZ)
R = 56 Ω
R= 100 Ω
R= 470 Ω
Precautions
1. The connecting wires should be straight and short.
2. If the amplitude of the output voltage of the oscillator changes with frequency, it must be
adjusted.
3. The values of inductance and capacitance are so selected that the natural frequency of the
circuit lies almost in the middle of the available frequency range.