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What is ohm's law

 Ohm's Law

This law, which is applicable to electrical conduction through reliable conductors, can be formulated as follows.

If the conductor's temperature is constant, the ratio of the potential difference (V) between any two places on it to the current (I) flowing between them will remain constant.

What I mean is, V/I = constant, or V/I  = R

where R is the resistance of the conductor between the two points considered.

Put in another way, It simply means that provided R is kept constant, current is directly proportional to the potential difference across the ends of a conductor. However, this linear relationship between V and I does not apply to all non-metallic conductors. For example, for silicon carbide, the relationship is given by V = KIm  where K and m are constants and m is less


 Example 1 :

A coil of copper has a resistance of 20 ohm at 10oC  and is connected to a 220 V supply. By how much must the voltage be Increased in order to maintain current constant if the temperature of the coil rises to 40oC? Take the tepmperature coefficient of resistance of copper as 0.00428 from 0oC

Solution:

first, we have to use this formula to calculate the resistance of the conductor after changing the temperature:

R40 ­/R­­­10­ = (1 + 40 x 0.00428) / (1 + 10 x 0.00428)

R40 = 20 x 1.1712/1.0428 = 22.5 ohm

After that, calculate the current at the initial temperature, which is at a temperature of 10oC

V/I  = R

I = V/R

I = 220/20 = 11 Ampere

Since, the wire resistance has become 22.5 Ohm at 40oC, the new voltage required for keeping the current constant at its previous value is

V/I  = R

V = I x R = 11 x 22.5 = 247.5

Increase in voltage required =  220 – 247.5 = 27.5 Volt


 Example 2 :

A coil of copper has a resistance of 20 ohm at 50oC  and is connected to a 240 V supply. By how much must the voltage be Decreased in order to maintain current constant if the coil temperature drops to 30oC ? Take the tepmperature coefficient of resistance of copper as 0.00428 from 0oC

 Solution:

first, we have to use this formula to calculate the resistance of the conductor after changing the temperature:

R30 ­/R­­­50­ = (1 + 30 x 0.00428) / (1 + 50 x 0.00428)

R30 = 20 x 1.1284/1.214 = 18.6 ohm

After that, calculate the current at the initial temperature, which is at a temperature of 50oC

V/I  = R

I = V/R

I = 240/20 = 12 Ampere

Since, the wire resistance has become 18.6 Ohm at 30oC, the new voltage required for keeping the current constant at its previous value is

V/I  = R

V = I x R = 12 x 18.6 = 223.2

Decrease in voltage required =  240 – 223.2 = 16.8 Volt

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