To study ohms law, firstly we have to understand some concepts.
1. Electric current:
Electric current is defined as flow of electric charge with respect to time is called electric current.Its SI unit is Ampere (A).
2. Voltage:
Battery or cell creates potential difference. It has two terminals , one is of high positive potential that is called an anode and another is at negative potential called cathode. When we place a charge particle between two terminals, the potential difference apply force on that charge particle and the charge particle moves corresponding to the electrode. Electrons moves toward positive electrode and protons moves towards negative electrodes.
In 1827, George Simon Ohm studied the relationship between voltage and current. That relationship is explained in the form of a famous law named Ohm’s law.
Statement:
Current flowing in the circuit is directly proportional to potential difference applied across it.
V ∝ I
V = IR
Where R is the proportionality constant called Resistance of the material.
Resistance is the property of material depend on geometrical configuration of that material.It has different values for conductors and insulators.
Si unit of resistance is Ohm (Ω). The symbol of resistor is as
Experimental proof:
The circuit diagram of ohms law is as
The circuit diagram consist of a resistor (Bulb, LED, heater), ammeter( to measure the electric current), voltmeter( to measure voltage across the resistor), variable voltage source.
All equipments are connected as shown in circuit diagram.
Increase the voltage with the help of variable voltage supply and note down values of voltage and current in voltmeter and ammeter respectively.
Observation table:
Voltage (V) |
Current (A) |
V/I |
2 |
0.5 |
4 |
4 |
1 |
4 |
6 |
1.5 |
4 |
8 |
2 |
4 |
10 |
2.5 |
4 |
12 |
3 |
4 |
We can easily calculate the value ratio V/I. The ratio V/I is always constant and that constant value is called resistance of that material.
You can also perform similar experiment using multiple batteries instead of variable voltage supply. From above data we can define the term 1 ohm.
If potential difference of 1 V is connected across resistor and due to that 1A current is flowing through that resistor then we say that the value of resistor is one ohm.
Question and Answer on OHM’s Law:
Q) If 10 V battery is connected across the resistor of 2 ohm then calculate current flowing through that resistor.
Q) Current flowing through 100 ohm resistor is 2 A. Calculate the value of voltage connected across the resistor.
Q) If 40 V voltage is connected across 1k (Ω), then calculate value of current.
Q) Complete the table.
Voltage V |
Current | Resistor |
2 | .0.2 |
—— |
10 |
—— |
1 |
—– |
1.5 |
40 |
—– |
3.5 |
10 |
Important Faq
Q.1) Which physical conditions of conductor should remain constant while studying Ohm’s law?
Answer: Following are the physical conditions which should remain constant or same while studying Ohm’s law,
- Length of conductor
- Area of cross – section of conductor
- Material of conductor
- Temperature of conductor
Q.2) What will the nature of graph between potential difference and current while studying Ohm’s law?
Answer: The graph between current and potential difference for a conducting substance is always a straight line and passes through origin.
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