Ohm's Law

by Jim McAlister, Black Box Video
© Black Box Video

PAGE BOOKMARKS

	The Ohm's Law says
	The Ohm's Law Formula
	Ohm's Law Symbol Shortcut
	Applications of Ohm's Law
	Quick Re-cap

The Ohm's Law says:

The current in a circuit is directly proportional to the applied voltage and inversely proportional to the amount of resistance.

Basically, this means that if the voltage goes up, the current flow will go up, and vice versa. Also, as the resistance goes up, the current goes down, and vice versa.

Current is affected by either voltage or resistance. If the voltage is high or the resistance is low, current will be high. If the voltage is low or the resistance is high, current will be low.

Resistance is not affected by either voltage or current. It is either too low, OK, or too high. If resistance is too low, current will be high at any voltage. If resistance is too high, current will be low if voltage is OK.

See - its simple!


	The Ohm's Law says

	The Ohm's Law Formula

	Ohm's Law Symbol Shortcut

	Applications of Ohm's Law

	Quick Re-cap


	Download in PDF format (will open in a new browser)

The Ohm's Law Formula:

When voltage is applied to an electrical circuit, current flows in the circuit. The following special relationship exists among the voltage, current and resistance within the circuit:

the size of the current that flows in a circuit varies in proportion to the voltage which is applied to the circuit, and in inverse proportion to the resistance through which it must pass

This relationship is called Ohm's Law and can be expressed as follows:

E	=	I x R

Voltage	=	Current x Resistance

E Voltage applied to circuit, in volts (V)

I Current flowing in the circuit, in amperes (A)

R Resistance in the circuit, in ohms Ω

In practical terms:

V	=	I x R

Voltage	=	Current x Resistance

1 volt will push 1 amp through 1 ohm of resistance

NOTE: E = IR, V = AR, or V= IR are all variations of the same formula. How you learned Ohm's law will determine which one you will use. Personal preference is the only difference; any one will get you the correct answer.

Ohm's Law Symbol Shortcut:

By using the Ohm's Law symbol below, anyone can remember the correct formula to use.

By knowing any two value you can work out the third. Simply put your finger over the portion of the symbol you are trying to calculate and you have your formula.

Applications of Ohm's Law:

As an application of Ohm's Law, any voltage V, current I, or resistance R in an electrical circuit can be determined without actually measuring it if the two other values are known.

This law can be used to determine the amount of current I flowing in the circuit when voltage V is applied to resistance R. As stated above, Ohm's Law is:

I	=	V
		R

Current	=	Voltage ÷ Resistance

In the following circuit, assume that resistance R is 2 and the voltage V that is applied is 12V. Then, current I flowing in the circuit can be determined as follows:

This law can also be used to determine the voltage V that is needed to permit current I to pass through resistance R:

I	=	V
		R

Current	=	Voltage ÷ Resistance

In the following circuit, assume that resistance R is 4 ohms. The voltage V that is necessary to permit a current I of 3A to pass through the resistance can be determined as follows:

Still another application of the law can be used to determine the resistance R when the voltage V which is applied to the circuit and current I flowing in the circuit are already known:

R	=	V
		I

Resistance	=	Voltage ÷ Current

In the following circuit, assume that a voltage V of 12V is applied to the circuit and current I of 4A flows in it. Then, the resistance value R of the resistance or load can be determined as follows:


	The Ohm's Law says

	The Ohm's Law Formula

	Ohm's Law Symbol Shortcut

	Applications of Ohm's Law

	Quick Re-cap


	Download in PDF format (will open in a new browser)

Quick Re-cap:


V = I x R	where V is in Volts	R	=	V I	I	=	V R
	where I is in amps
	where R is in ohms


P = V x I	where P is in watts	I	=	P V	V	=	P I
	where V is in Volts
	where I is in amps


P = 1² R