One of the most common tasks you can face in the 10th-grade physics or science laboratory is to perform the Ohm’s Law Experiment. It is common in class IX or class X in most boards like CBSE, ICSE, state boards, and even in IGCSE or IB curriculums. This experiment is also there for certain class 12 syllabus.

We have covered the  theory of Ohm’s law experiment before, now let’s move on to the practical session of verifying Ohm’s law. But first, let’s state Ohm’s law for convenience’s sake once.

Ohm’s Law

The current through a conductor between two points is directly proportional to the voltage across the two points.

Ohm’s Law Mathematical Expression

V = IR

Where,

• V = voltage across a given conductor
• I = current through the circuit
• R = resistance of the conductor

Base Idea of the Experiment

Here V would be measured across the conductor, and I would be measured in series to it. We will change the voltage, and record the current as a result. When we have a bunch of readings, we will plot the readings in a graph. 

Our intention is to see if the graph would come out as close to a straight line as possible. That would mean that the resistance remained the same, denoting V was proportional to I. When we see that V and I are proportional, we will get the value of the resistance from the above formula.

The Experiment

Equipment

To perform the Ohm’s law experiment, you will need the following equipment:

• 1 battery eliminator (0-12 volts, 2 Amps)
• 1 voltmeter 
• 1 ammeter
• 1 rheostat
• 1 resistance box (or an unknown resistor)
• Connecting wires

You can find all of those in Labkafe’s  Composite Lab Package or  Physics Lab Package .

Procedure

We will need to build an electronic circuit with the battery and the resistor, through which the current is supposed to pass. To measure that current, you will need to connect the ammeter in between the battery and the resistor in series. And to measure the voltage, you will have to connect the voltmeter in parallel to the resistor.

• Why do you need to connect the ammeter in series?
  • Since the ammeter measures the current passing through the circuit, that is why it has to be a part of the circuit itself. That means, you will have to connect the positive (red) pole of the battery to the negative (black) pole of the ammeter, and connect the positive pole of the ammeter to the rest of the circuit. Since an ideal ammeter has ZERO resistance, we can assume that there will be no loss of current across the ammeter itself.

Read more:  how does an ammeter work?

• Why do you need to connect the voltmeter in parallel?
  • A voltmeter is supposed to measure the potential difference between two points in a circuit. Therefore, the voltmeter needs to touch those two points simultaneously with its two points, making a parallel circuit with that part of the system. Since an ideal voltmeter has INFINITE resistance, it will eat up next to no current across itself, making sure it does not influence the system.

Read more:  working principles of a voltmeter

Ideally, we should be using a battery that can give different voltages that our experiment needs. But no batteries in reality do that. So, we will put a rheostat in series with the battery, which then we can use to control the voltage as we wish. 

• How can a rheostat control the voltage when a resistor is supposed to change the current?
  • A rheostat is also a resistor, just one that varies in power. So, you may naturally ask how a resistor is controlling voltage while they are supposed to control the current? The answer is quite simple ‒ just look again at the Ohm’s law formula. In “V = IR” we take R constant. But for a given, fixed value of current (keeping I constant), if we change the resistance value (varying R), the voltage V will change. This is a clever manipulation of Ohm’s law principle.

Even though our battery eliminator (which we are using instead of a real battery) can supply different amounts of voltage, we will keep it fixed at a constant voltage and use the rheostat to change the voltage. This will be as close to real-life as possible.

Setting Up

The circuit diagram for the Ohm’s law experiment is like the following:

Where,

• A is the ammeter
• V is the voltmeter
• B is the battery
• Rh is the rheostat
• R is the resistor
• B’ is the virtual, variable battery we are creating by combining B and Rh 
• S is a switch turning the circuit on and off (you may already have a switch in your battery eliminator to serve the same purpose)

(Note: the diagram in your textbook may differ somewhat from our diagram. But don’t worry, it will work out fine for our purpose.)

How to perform the experiment

1. Connect the equipment as shown in the circuit diagram. Keep the switch off for now and the rheostat at the least position.
2. Take a notebook and make two columns for voltage (V) and current (I). 
3. Turn on the switch.
4. Observe the voltmeter and ammeter carefully. In the notebook, note down the values shown in the meters in the respective columns for V and I. 
5. Turn off the power and move the rheostat to change its resistance a little. This will change the reading in the voltmeter.
6. Repeat steps 3, 4 and 5 a few more times till you get at least half a dozen different readings.
7. Plot the V vs I graph in a fresh graph paper. What does the graph look like? 

Interpreting the Results

We have performed the Ohm’s law experiment with our electronics lab package, and here is the result data as chart and graph:

As you can see, the above data shows that the current rose steadily as the voltage increased and we had a pretty much straight lined graph. That means I was proportional to V. Proved!

Finding the resistance of the conductor

Since V = IR,

So, R = V/I

From the above results, we can figure the average voltage as, V =  3.96v

And the average current was, I = 0.203A

Therefore, the effective value of the resistor in the experiment would be: 

R = V/I = 3.96/0.203 = 19.53Ω.

How accurate are the results of Ohm’s Law experiment?

In reality, we used a 19 ohms resistor for the experiment. The error (0.53 ohms) probably came due to: 

• Heating issues during the Ohm’s law experiment
• Internal resistances of the voltmeter, ammeter, or other components
• The equipment being used not precisely perfect to theory

Do keep in mind that due to various natural issues it would be hard for you to get an accurate value of the resistor ‒ there can probably be a ~10% error margin. The older your equipment is, the more error you can expect.

All the equipment used in this experiment came from Labkafe’s standard composite lab package.

The post How to Perform Ohm’s Law Experiment for Class 10 | Labkafe appeared first on Labkafe Blog.

To find the weight of a given body (Wooden Block) using parallelogram law of vectors.

Apparatus:

1. Parallelogram Apparatus (Gravesand’s Apparatus)
2. Two Slotted Weights  With Hanger
3. Wooden Block With Hook
4. Spring Balance
5. Mirror Strip
6. Cotton Thread (roll)
7. Drawing Pin

Theory :

In Fig. 5.1 we see the Gravesand’s apparatus or Parallelogram apparatus.  It consists of a wooden board A fixed vertically on two pillars. There are two pulleys P and Q fitted at the same level at the top of the board. Three set of slotted weights are supplied with the apparatus which can be used to verify the parallelogram law of vectors.  A thread carrying hangers for addition of slotted weights is made to pass over the pulleys so that two forces P and Q can be applied by adding weights in the hangers. By suspending the given object, whose weight is to be determined, in the middle of the thread, a third force W is applied.

Fig 5.1

If  two vectors acting simultaneously on a particle are represented in magnitude and direction by the two adjacent sides of a parallelogram drawn from a point, then their resultant is completely represented in magnitude and direction by the diagonal of that parallelogram drawn from that point.

Let two vectors  (P) ⃗  and (Q) ⃗  act simultaneously on a particle O at an angle θ as shown in figure 5.2. They are represented in magnitude and direction by the adjacent sides OA and OB of a parallelogram OACB drawn from a point O. Then the diagonal OC, will represent the resultant R in magnitude and direction. Mathematically we can say, 

(R) ⃗= (P) ⃗ + (Q) ⃗

If a body of unknown weight W is suspended from the middle hanger and balancing weights P and Q are suspended from other two hangers then, (R) ⃗ and the three vectors (P) ⃗,(Q) ⃗ ,(W) ⃗  are in equilibrium. Under equilibrium  |W| ⃗= |R| ⃗. Weight of a body is a force.

Hence, |W| ⃗ = |P| ⃗+|Q| ⃗.

Equation 1

or,                     

If S is the actual weight of the body, then the percentage error in the experiment can be calculated using 

Equation 2

Procedure :

1. Set the Gravesand’s apparatus with its board in vertical position with the help of plumb line.
2. Ensure that the pulleys are moving smoothly. Oil them if necessary.
3. Fix a drawing paper sheet on the board with the help of drawing pins.
4. Take a long thread and tie two hangers H1 and H2 to the both ends of the thread.
5. Tie the given body B, whose weight is to be found, with one end of another shorter thread.
6. Tie the other end of the shorter thread in the middle of the longer thread to form a small knot, O. This knot becomes the junction of the three threads.
7. Pass the longer threads over the two pulley P1 and P2 of the apparatus and place two equal slotted weights P and Q the hangers H1 and H2 .
8. The body B is made to hang vertically with the knot O somewhere in the drawing paper.
9. Adjust the weights P and Q to keep the knot O at a position slightly below the middle of the paper. This is the equilibrium position of O. Ensure that all the weights hang freely and do not touch the board.
10. Mark the position of junction O on the white paper by a pencil.
11. Ensure that there is no friction at the two pulleys P1 and P2. For that purpose, disturb the positions of P and Q a little and leave them. The knot should go back to its initial equilibrium position, If it does not, oil the pulleys to remove friction.
12. Mark the position of the equilibrium of the knot (O) by a dot of a pencil on the paper sheet.
13. Take the thin mirror strip m and place it breadthwise on the paper under one of the threads.  See the image of the thread in the mirror. Adjust your line of sight such that it is at right angle to strip and the thread. At this point cannot see the image of the thread (meaning, parallax is removed). Mark two points P1 and P2 on the paper, on either side of the strip exactly behind the thread.
14. Similarly, mark two points Q1, Q2 and W1, W2 for the other two threads.
15. Remove the threads and hangers from the apparatus and note the weights of the two hanger H1 and H2 along with the slotted weights in table 5.1. Let these two weights be P and Q.
16. Remove the paper from the board and join P1 and P2, Q1, Q2 are W1, W2 with the help of ruler to get three lines which should meet O. These three lines represent the directions of three forces.
17. To represent the vector, chose a suitable scale, say 10 gm (0.1N) = 1 cm.
18. Cut the lines OA and OB to represent the forces  and  respectively. For example, if P = 60 gm and Q = 60 gm, then OA = 6 cm and OB = 6 cm.
19. With OA and OB as adjacent sides, complete the parallelogram OACB as shown in fig 5.2.
20. Join O and C. The length OC represents the resultant vector  which corresponds to the unknown weight W.
21. Measure OC (l) and multiply it by the scale (10 g) to get the value of R.
22. Measure the angle  () using a protractor and calculate W using equation (i).
23. Repeat the experiment with fresh paper and using different weights (un-equal) P and Q in the hangers.
24. Find the calculated value of weight R.
25. Measure the actual weight (S) of the unknown weight (W) by the spring balance and calculate the percentage error using equation (ii).

Observation:

Least count of spring balance, L.C. = _______________ gm

Weight of B by spring balance, S = ________________gm

Scale factor: Let ______ cm = ___________gm

Table 5.1 Measurement of weight of given body

Calculations:

Result:

For equal weights

Weight of unknown body by observation, W: ……………………….

Weight of unknown body by calculation, W‘: ……………………….

For un-equal weights

Weight of unknown body by observation, W: ……………………….

Weight of unknown body by observation, W‘: ……………………….

Precautions :

1. The pulleys should be frictionless.
2. The boards should be stable and vertical.
3. The hangers should not touch the board.
4. There should be one central knot and it should be small.
5. When the lines of action of the forces are marked, the hangers should at rest.
6. The scale should be so chosen that a fairly large parallelogram is obtained.
7. Threads should be strong and thin, so that they may be regarded as massless.

Reference:

1. http://www.ncert.nic.in/
2. https://www.learncbse.in/

You may check out our blog on BEAM BALANCE

About Labkafe: Lab Equipment Manufacturer & Exporter

We are a School laboratory furniture and Lab equipment manufacturer and supplier. In laboratory furniture for school, we first design the entire laboratory room keeping in mind the requirements as per affiliation CBSE Bye-Laws. Also, we take care of the complete designing and installation of laboratory furniture.

In the lab equipment section, we have a wide range of glassware, chemicals, equipment and other lab accessories. Most of them are available for order online on our website but some of them can be procured on demand.

If you have need:-

• laboratory equipment or lab furniture requirements for school
• composite lab equipment list for school
• Physics lab equipment list for school
• Chemistry lab equipment list for
• Biology lab equipment list for school
• Pharmacy lab equipment

do drop a message through chat or mail us at sales@labkafe.com or whatsapp +919147163562 and we’ll get in touch with you.

The post Parallelogram Triangle Law of vector addition Experiment Class 11 | Gravesand’s apparatus appeared first on Labkafe Blog.

Aim:

To study variation of time period of a simple pendulum experiment physics practical of a given length by taking bobs of same size but different masses and interpret the result.

Apparatus:

1. A Clamp With Stand
2. Bob with Hook of Different Masses
3. Split Cork
4. Stop Clock/Stop Watch
5. Vernier Callipers
6. Cotton Thread
7. Half Meter Scale

Theory:

See Experiment 6.

The time period (T) of a simple pendulum for oscillations of small amplitude, is given by the relation,

T = 2π√(L/g) or T2 = (4π2/g) × L

∴ T ∞√L and T ∞ 1/(√g)

From the above equation, it clearly indicates that the time period of a simple pendulum is independent of mass i.e. for the same value of L and g, the time period of two bobs of different masses will be the same.

Procedure:

1. Choose any three bobs of known masses and determine their radius as in Experiment 1.
2. Now, arrange the experiment set up for first bob (say mass m1) with any effective length of simple pendulum (say 90 cm) as explained in Experiment 6. The effective length of the simple pendulum will be kept same in each case.
3. Record average time taken for 20 or 25 oscillations by the simple pendulum by performing step 4 to 15 as explained in Experiment 6.
4. Calculate the time periods for each bob and record them in table 7.1.

Observations:

Vernier constant

Vernier constant of the vernier callipers, V.C. = ______________ cm

Zero error, ±e = _____________cm

Least count of stop clock = ____________s

Zero error of stop clock = ___________s

Table 7.1 Determination of time-periods for same lengths of the different pendulum.

Graph:

See Experiment 6.
 

Result:

               For the same value of effective length and acceleration due to gravity, the time period of bobs for different masses are same.

Precautions :

1. The thread should be very light and strong.
2. The point of suspension should be reasonably rigid.
3. The pendulum should oscillate in the vertical plane without any spin motion.
4. The floor of the laboratory should not have vibration, which may cause a deviation from the regular oscillation of the pendulum.
5. The amplitude of vibration should be small (less than 15) .
6. The length of the pendulum should be as large as possible in the given situation.’
7. Determination of time for 20 or more oscillations should be carefully taken and repeated for at least three times.
8. There must not be strong wind blowing during the experiment.

Reference:

1. http://www.ncert.nic.in/
2. https://www.learncbse.in/

About Labkafe: Lab Equipment Manufacturer & Exporter

We are a School laboratory furniture and Lab equipment manufacturer and supplier. In laboratory furniture for school, we first design the entire laboratory room keeping in mind the requirements as per affiliation CBSE Bye-Laws. Also, we take care of the complete designing and installation of laboratory furniture.

In the lab equipment section, we have a wide range of glassware, chemicals, equipment and other lab accessories. Most of them are available for order online on our website but some of them can be procured on demand.

If you have need:-

• laboratory equipment or lab furniture requirements for school
• composite lab equipment list for school
• Physics lab equipment list for school
• Chemistry lab equipment list for
• Biology lab equipment list for school
• Pharmacy lab equipment

do drop a message through chat or mail us at sales@labkafe.com or call +919147163562 and we’ll get in touch with you.

The post Simple Pendulum Experiment Physics Practical Class 11 and 9 | Labkafe appeared first on Labkafe Blog.