LEXPERIMENTAL PHYSICS

 

Ohm's law

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Luciano Troilo, created with GeoGebra

ACTIVITY

  • Click the button "change resistor" to generate a random resistance between 1000Ω and 2000Ω
  • Moves the cursor of the power supply slider and read the voltage across the resistor and the current flowing through it.
  • Repeat the measurement several times.
  • Transfer the experimental data to an Excel spreadsheet and analyse the results.
  • Prove the validity of Ohm's law:

The voltage across a resistor is directly proportional to the amount of electric current through it (for any given temperatur).

V \propto I

Introducing the constant of proportionality, the resistance, one arrives at the usual mathematical equation that describes this relationship:

V=R*I

Click here to download and see an example

 

the electric circuit

how you build it

 

THEORY

Ohm's law is an empirical law relating the voltage V across an element to the current I through it:
V \propto I
(V is directly proportional to I). This law is not always true: For example, it is false for diodes, batteries, etc. However, it is true to a very good approximation for wires and resistors (assuming that other conditions, including temperature, are held fixed). Materials or objects where Ohm's law is true are called "ohmic".

How can you remember the formulas

Cover with a finger, the symbol of the electric quantity that you search and then read the formula
All formulas that link, resistance, current, voltage and power in a resistor

Unit of measurement:

physical quantity
symbol
unit of measurement
unit abbreviation
definition
voltage (electrical potential difference)

E or V

volt

V

1V:  the work which would have to be done to move the charge of 1 coulomb between two points is equal to 1 joule
current

I

ampère

A

1A: charge flowing through some surface at the rate of one coulomb per second.
resistance

R

ohm

Ω

1 Ω:  resistance between two points of a conductor when a constant potential difference of 1 volt, applied to these points, produces in the conductor a current of 1 ampere

 

PROBLEMS/EXERCISES

UNDER CONSTRUCTION ( please insert here some problems and/or exercises

THE END

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