# Lesson Notes By Weeks and Term - Senior Secondary 1

Verification of Ohm's law (Practical)

Term: 2nd Term

Week: 7

Class: Senior Secondary School 1

Age: 15 years

Duration: 40 minutes of 5 periods each

Date:

Subject:      Physics

Topic:-       Verification of Ohm’s law(Practical)

SPECIFIC OBJECTIVES: At the end of the lesson, pupils should be able to

1. Solve some exercises on workdone and power
2. Carry out an experiment to verify the ohm’s law

INSTRUCTIONAL TECHNIQUES: Identification, explanation, questions and answers, demonstration, videos from source

INSTRUCTIONAL MATERIALS: Videos, loud speaker, textbook, pictures

INSTRUCTIONAL PROCEDURES

PERIOD 1-2

 PRESENTATION TEACHER’S ACTIVITY STUDENT’S ACTIVITY STEP 1 INTRODUCTION The teacher reviews the previous lesson on Ohm’s law Students pay attention STEP 2 EXPLANATION He solves some exercises on workdone and power Students pay attention and participates STEP 3 DEMONSTRATION He explains and carries out an experiment to verify the ohms law Students pay attention and participate STEP 4 NOTE TAKING The teacher writes a summarized note on the board The students copy the note in their books

NOTE

VERIFICATION OF OHM’S LAW

The ammeter which measures the current flowing through the metallic conductor (Constant wire) is connected in series with the wire and the cell. The voltmeter is connected in parallel with the conductor and measures the p.d. across it. The rheostat is used to vary the current flowing in the circuit.

We cause the current to flow by pressing down the switch. The graph of V against I is plotted and a straight line graph passing through the origin is observed. The slope gives the resistance of the wire.

Graph of Voltage (V) against Current (I)

Slope (S) = ΔπΔπΌ = π2− π1πΌ2− πΌ1

Slope (S) = Resistance (R).

WORK DONE IN ELECTRIC CIRCUIT/ ELECTRICAL ENERGY

Work done when electricity flows from one point to another of different potential is given by

W= QV

The Unit is Joule = Coulomb x Volt

Since Q = It

Therefore, W= QV = IVt

From ohms law, V= IR

:. W= QV

1. W = IVt
2. W = I2Rt
3. W  =  V2 T

R

ELECTRICAL POWER

Power (P) is define the time rate of doing work.

P = ππππππππ/πΈπππππ¦ πππ π ππππ‘π(π½ππ’πππ )

ππππ π‘ππππ (πππππππ )

Electrical power is the amount of electrical work done or electrical energy dissipated per second.

P = IVt

t

Therefore, P= IV

Power P = IV = I2R = V2

R

Unit of power is Watt (W).

Large units of power are kilowatt (KW) and Megawatt (MW)

1kw = 1000 watts

1MW=106W=103KW

Example: Calculate the Electrical energy and Power Used by an electric Heater of 11β¦ when the voltage source is 220V ac source for 2seconds

Solution:

Resistance R = 11β¦

Voltage V = 220V

Time t = 2s

Electrical energy =

= 2202 x 2

11

= 8800J = 8.8KJ

Power = ππππππππ / πΈπππππ¦

ππππ π‘ππππ

=    π2

π

= 8800

2

= 4400w

= 4.4KW

PRACTICAL

VERIFICATION OF OHM’S LAW USING STANDARD RESISTOR (2Ω), AMMETER (0-2A), CONNECTING WIRES AND VOLTMETER.

MATERIALS REQUIRED :

A resistor of about 5 Ω,

an ammeter ( 0 - 3 A),

a voltmeter (0 - 10 V),

four dry cells of 1.5 V each with a cell holder (or a battery eliminator),

a plug key,

connecting wires,

and a piece of sand paper.

PRECAUTIONS :

• All the electrical connections must be neat and tight.
• Voltmeter and Ammeter must be of proper range.
• The key should be inserted only while taking readings.

CIRCUIT DIAGRAM:

PROCEDURE :

1. Draw the circuit diagram as shown above.
2. Arrange the apparatus as per the circuit diagram.
3. Clean the ends of the connecting wires with sand paper and make them shiny.
4. Make the connections as per circuit diagram. All connections must be neat and tight. Take care to connect the ammeter and voltmeter with their correct polarity. (+ve to +ve and -ve to -ve).
5. Determine the zero error and least count of the ammeter and voltmeter and record them.
6. Adjust the rheostat to pass a low current.
7. Insert the key K and slide the rheostat contact to see whether the ammeter and voltmeter are showing deflections properly.
8. Adjust the rheostat to get a small deflection in ammeter and voltmeter.
9. Record the readings of the ammeter and voltmeter.
11. Plot a graph with Valong x-axis and I along y-axis.
12. The graph will be a straight line which verifies Ohm's law.
13. Determine the slope of the V-I graph. The reciprocal of the slope gives resistance of the wire.

OBSERVATIONS:

• Range of the given ammeter=.................... A.
• Least count of the given ammeter = ..................... A.
• Range of the given voltmeter = .....................V.
• Least count of the given voltmeter = .....................V.
• Mean value of V/I from observations, R = .......... Ω.

Observation from graph:

• Slope of I vs V graph = ...........
• R from graph = 1/ slope = .............. Ω.

Observation table:

As performed in the simulator:

1. Click on Show Labelcheckbox to label/unlabel the apparatus in the circuit.
2. Click on Show Helpcheckbox to show/hide the 'help' for performing the lab.
3. Click on the Observation Table tab below to open the Observation table.
4. Drag the plug key to switch on/off the current.
5. Adjust the rheostat such that ammeter shows the low value of Current (I). Note corresponding voltmeter reading.
6. Increase the current by adjusting the slider of the rheostat and take about 5 or 6 sets of readings.
7. Note carefully ammeter and voltmeter readings in each set and record in the Observation Table.
8. Note V/Iratio for each set of reading in the Resistance
9. Click on Plot Graphbutton to plot voltmeter readings (V) along the x-axis and the corresponding ammeter readings (I) along the y-axis in the graph.

EVALUATION:   1. A box is pulled with a force of 25N to produce a displacement of 15m. If the angle between the force and displacement is 30Λ, find the work done by the force.

1. During braking, a force of 2000N is applied to the brakes of a car. The car takes 20m to come to a stop. Calculate the work done
2. An electric machine makes use of 300 J of energy to do work in 10s. How much power does it use?
3. John is who has a mass of 60 kg runs up to 12m high in 40 seconds. Compute his power.

CLASSWORK: As in evaluation

CONCLUSION: The teacher commends the students positively