`Good Hope English Medium School

Group 3 (Avogadros)Class : X

Presented By,,

Members of Group 3 (Avogadros)

Vijay Das P Adish Assäin Akhila Aniyan Renna Jan Fathima Hiba Sherin K Lal

Ohm’s Law

Georg Simon Ohm

Ohm, who was born at Erlangen in Germany, seems to have acquired his interest in science from his father, a skilled mechanic.

Georg Simon Ohm, was a German physicist, best known for his “Ohm’s Law”.

The physical unit of electrical resistance, the Ohm, was named after him.

He studied at the University of Erlangen and then taught at the Cologne Polytechnic in 1817.

He was working on the manuscript of his textbook on optics when he died on July 6, 1854.

Ohm also worked on sound, suggesting in 1843 that the ear analyzes complex sounds into a combination of pure tones. This result was rediscovered by Hermann von Helmholtz in 1860.

He achieved his lifelong dream, a position with a major university, in 1849 as professor at the University of Munich.

Current flow through an ideal conductor is directly proportional to the potential difference (voltage) and inversely proportional to the resistance.

Conductor is also known as a resistor. An ideal conductor is a material whose resistance does not change with temperature.

For an ohmic device,

Voltage Current Resistance

V I RV = Voltage I = Current (Amperes = A)R = Resistance (Ohms = Ω)

Ohm’s Law

Conventional Current: (the current in electrical circuits) Flow of current from positive terminal to the negative terminal. - has units of Amperes (A) and is measured using ammeters.

Voltage: Energy required to move a charge from one point to another. - has units of Volts (V) and is measured using voltmeters.

Current and Voltage Defined

Metals obey Ohm’s Law linearly so long as their temperature is held constant. Their resistance values do not fluctuate with temperature, i.e. the resistance for each resistor is a constant

Most ohmic resistors will behave non-linearly outside of a given range of temperature, pressure, etc.

Ohmic Resistors

Voltage and Current Relationship for Linear

ResistorsVoltage versus Current for a 10 ohm Resistor

00.10.20.30.40.50.6

0 1 2 3 4 5 6

Voltage (V)

Cur

rent

(A)

Voltage and current are linear when resistance is held constant.

Ohm’s Law continued

The total resistance of a circuit is dependant on the number of resistors in the circuit and their

configuration

1 2

1 2

...

1 1 1 1 ...

total

total

R R R R

R R R R

Series Circuit

Parallel Circuit

Ohm’s Law continued

Series Circuit

Current is constant

Why?Because only one path for

the current to take

1 2 3

1 2 3

1 2 3

V V V VI I I IR R R R V I R

1 1 2 2 3 3

1 2 3

1 2 3

1 2 3

1 2 3

V I R V I R V I RR R R R

V V V VV I R I R I R

V I R R R

V I R

Series Equivalent Circuit

1 2 3

1 2 3 1 23

23 2 3

1 2 3

where 1 1 1 1

V V V VI I I I I I

I I I

R R R R

Voltage is constant Why?

Because there are 3 closed loops in the circuit

V I R

Parallel Circuit

Parallel Equivalent Circuits

231 2 3 2 3 1 23

123 1 2 3123 1 23

1 2 31 2 3

1 2 3 1 2 3

1 1 1 1 1 1 1 1 1 1

1 1 1 1

11 1 1 1 1 1

let so

and

R R R R R R R R R R

R R I I I IR R R R

I I IV I R I I I

R R R R R R

Now you get to try some experiments of your own, but first, a quick tutorial on the equipment

you will be using

You’re turn to do some experiments!

- Voltmeter- Ammeter- Breadboard- Potential Divider- Resistors- 9V battery

Let’s do a quick review…

The equipments you’ll be using:

Voltmeter:Connect either end of the meter to each side of the resistor

If you are reading a negative value, you have the probes switched.

There should be no continuity beeping. If you hear beeping, STOP what you are doing and ask someone for help!

How to use a voltmeter:

Voltmeter

Voltage:Probes connect to either side of the resistor

Measuring Voltage

You encountered breadboards early in the year. Let’s review them:

Breadboards

The breadboard

How the holes on the top of the board are connected:

SeriesResistors are connected such that the current can only take one path

ParallelResistors are connected such that the current can take multiple paths

Experiment 1 – Ohm’s Law

Click on the black box to watch the video

In reality, the data we get is not the same as what we get in theory.

Why?

Because when we calculate numbers in theory, we are dealing with an ideal system. In reality there are sources of error in every aspect, which make our

numbers imperfect.

Real data

ConclusionOhmic resistors obey Ohm’s Law linearly

Resistance is affected by temperature. The resistance of a conductor increases as its temperature increases.

V I R

Thank You for Watching!