how do you find resistance in a light bulb?

Question

What is the resistance of a 60 watt light bulb designed for 120 Volts?
*I used r= v/i but I just keep getting confused.

Answer 1

R = resistance:

If you need to know the Resistance in Ohms you can divide the Voltage (E) by the Current (I) in Amperes or, divide the square of the voltage by the Power in Watts or Voltamps, or you can divide the Power in watts by the square of the current in Amps.

Answer 2

In all there are four equations relating to V across, I through and P in a device having a resistance R = V/I[Ohm's Law]; P = VI or V^2/R or I^2R. One can use any of the above formulae correctly and get the answer. But one should not do it mechanically but by understanding it. Firstly one must understand that R is really the property of the device and does not depend upon the external parameter voltage which decides how much current will flow through it and P is the corresponding power produced. Wattage is not really the property of the bulb at all. But it is a property which depends on the voltage applied. That is why saying that a bulb is 60 W is meaningless unless we say at what voltage. That voltage has been given as 120 in this problem. So choose the appropriate equation above to get R. That happens to be P = V^2 /R which gives R as V^2/P [120x120]/60 = 240 Ohm. You can use R V/I provided you know I. You can find I for which 60 w power is produced in the bulb when 120 volts are applied to it buy using the equation P = VI which gives I = P/V = 60/120 = 0.5 A. Now you can use R = V/I and get 120/0.5 = 240 ohm. you can try to use all the above formulae to get the same answer. but remember that R is really the property of the bulb independent of anything else.

Answer 3

Use ohm's law.

Resistance = voltage / amps

Now we must first figure out the amps. Since a watt = votage * amps a 60 watt bulb is
60 = 120 * amps
amps = 60/120
amps = 1/2

So now we know the bulb uses 1/2 amps and 120 volts, now all we must do is plug it into the ohm's law equation to get the resistance:
Resistance = voltage / amps
Resistance = 120 / .5
Resistance = 240 ohms

Answer 4

The equation R=V/I requires you to know the current. You are given the wattage (60). Here's another useful relationship:

W = V x I

The current of a 60 watt bulb at 120V is 0.5 amps. Now you can use that data:

R = V / I = 120/0.5 = 240 ohms

Answer 5

You also need the equation for power, P = VI , now eliminate the I from the two equations that you have and you get P = V^2/R so you can figure the R = V^2/P

This should solve your problem since you know the power P = 60 and V = 120.

Answer 6

you have to use the power equation

ohms law is r=v/i

power is w=i*v so i which is current is w/v or 60/120 equals .5 amps
so 120/ .5 amps =r which is 240 ohms