How do you calculate resistance in electric circuits?

Answer 1

The easiest way to measure ohms is with an ohm meter, which is typically part of an electrical multi-meter. A multi-meter can read many different kinds of electrical variables: AC voltage, DC voltage, amps, and ohms among them.

Answer 2

Ohm's law :

I=V/R

(I = current in amperes, V = potential in volts, R = resistance in ohms)

Using Ohm's law and the mathematical laws of equality, one can calculate the value of any one of these three properties given the other two are known.

A 40watt 120volt light-bulb draws 0.335 amps (Watts = Amps x Volts). Using Ohm's law we can find the resistance value of said light-bulb:

I=V/R = R=V/I = R=120/0.335 = R=358

This will work with any electrical circuit. (Note, a 120v household light-bulb is designed to use resistance to produce heat, when the filament is heated resistance is greatly increased. The watts rating on a bulb is for nominal running tepmeratures. When cold, the resistance across the filament is much less.)

Also, a good site for if you are stuck of GCSE or pre-GCSE Physics is BBC Bitesize, which comes complete with fun tests, colourful clicking-games and easy, fast tutorials.

Resistance is measured in the standard units of ohms using the omega symbol

Answer 3

You look at the color bands. There are three or four bands, sometimes five. The first two bands indicate the first two digits of the value, the third band indicates the multiplier, the fourth band indicates the tolerance, and the fifth band is used for temperature coefficient.

0 - Black

1 - Brown

2 - Red

3 - Orange

4 - Yellow

5 - Green

6 - Blue

7 - Violet

8 - Grey

9 - White

Take the first two bands and write the number down. Lets say the resistor was red - violet - orange. You would write down 27. The third band would be the multiplier, in the form 10N, so you would write down that many zeros after the 27, giving you 27000, or 27 KOhms.

If the third band is gold is silver, then the multiplier is a divider, gold being 0.1 and silver being 0.01, so a brown - red - gold resistor is 1.2 ohms, while a brown - red - silver resistor is 0.12 ohms.

If the fourth band is missing, the tolerance is 20%. If it is silver, the tolerance is 10%. If it is gold, it is 5%.

These are the basics. For more information, please see the Related Link below.

Answer 4

A resistor use a color code or an alpha-numeric code to identify its resistance. The color code is a series of colored bands, the sequence of which identify the value of its resistance (you can check this out, in detail, on the internet). The alpha-numeric code uses letters to identify the multiplication factor (e.g. R = x1, K = x1000, M = x1 000 000) and the position of the letter to indicate the decimal point. For example,

R10 = 0.10 ohm

1R0 = 1.0 ohm

10R0 = 10.0 ohm

etc.

Answer 5

E = I x R

Thus R (in ohms) = E (in volts) / I (in amps)

Answer 6

Resistance = Volts / Current