The problem statement, all variables and given/known data - we wish to measure t

Question

The problem statement, all variables and given/known data - we wish to measure the resistance of a lit light bulb. Unfortunately, the resistance of the light bulb when hot is not the same as when it is cold. when the light bulb is turned on it becomes hot. we cannot easily measure the resistance of the light bulb when it is on (hot) because if we use an ohmmeter to measure the resistance when the light bulb is lit, we are really measuring the resistance of the whole circuit, not that of the light bulb only. however, we can approximate its value by replacing the light bulb with a variable resistor. adjust the variable resistor to obtain the same value of the current measured with the good batteries. Now disconnect the variable resistor from the circuit and measure its resistance using an ohmmeter. also, measure the resistance of the cold light bulb with the ohmmeter using the same connection.

The question - you measured the resistance of the flashlight when it had no current passing through it. the resistance of the flashlight is different, however, when current is passing through it. explain how your measurement of the resistance of the variable resistor is a valid approximation of the resistance of the flashlight when it had current passing through it. is the resistance higher when the flashlight is on or off?

My data - resistance of variable resister - 3.3 Ohms

Resistance of cold light bulb - 1.5 Ohms

please help.

Explanation / Answer

Resistance of cold light bulb when no current is flowing through it is 1.5 Ohm

Now as bulb gets hotter as current is supplied through it so hard to measure resistance

so, it is replaced by a variable resistance its value is changed to a certain value which will ensure flow of same amount of current as it was when bulb was on

as voltage is same => resistance of variable resistor is same as that of bulb while on

and from data we get it to be 3.3 ohm which is higher than when it was cold

=> resistance increases with increase in temperature

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