# Voltage and Current Related to Power

Discussion in 'General Electronics Chat' started by mkevil, Feb 16, 2014.

1. ### mkevil Thread Starter New Member

Feb 14, 2014
2
0
Suppose I have two circuits which consist of a battery, a light bulb(with very high internal resistance in circuit A, very low in B) and the wire.

Circuit A:

I = 1.60217657 × 10^-20 Amps (Single electron every 10 seconds!)
Voltage = 10^21 Volts
Internal Resistance of the Bulb: Very High (it's an imaginary bulb anyway)

Circuit B:

I = 10^21 Amps
Voltage = 1.60217657 × 10^-20 Volts
Internal Resistance of the Bulb: Very Low

Do both light bulbs have same brightness? (The exact question is: Is there any difference in two light bulbs except for the resistance? Like blinking / not working at all etc)

I am a newbie and I thought on every component, it's only watts that matters but they don't seem to be the same in Proteus.

2. ### #12 Expert

Nov 30, 2010
16,685
7,325
Light bulbs depend on the temperature of the filament. No two light bulb designs are going to act the same. You have set up an equal power scenario, but light bulbs are absolutely the wrong thing to measure with. This is like asking if a scared turtle is using more energy than a sleeping cow.

3. ### bwilliams60 Active Member

Nov 18, 2012
734
94
I thought I already learned enough here today but I guess I will be humbled one more time before I hit the hay. So voltage and amperage of these two bulbs are the inverse of each other and therefore power would have to be the same. If this is a working circuit, and it would have to be because you have current flow, wouldn't the working resistance have to be the same? Resistance with the bulbs turned off could be entirely different because of temperature, I get that, but wouldn't they be the same for this scenario under operation?

4. ### shteii01 AAC Fanatic!

Feb 19, 2010
3,501
511
Ok, lets crunch some numbers:

Case 1.
V=10 volts
I=0.001 A
Power=VI=10*0.001=0.01 W
Resistance=V/I=10/0.001=10,000 Ohm=10 kOhm

Case 2.
V=0.001 volts
I=10 A
Power=VI=0.001*10=0.01 W
Resistance=V/I=0.001/10=0.0001 Ohm

Conclusion: Power is the same. Resistances are not the same.

5. ### #12 Expert

Nov 30, 2010
16,685
7,325
No, the working resistance will not be the same.

A 3 volt bulb that operates with 1 amp of current has 3 ohms.
A 1 volt bulb that operates with 3 amps of current has 1/3 ohm.
You can run powers of ten in both directions, but you will never hit two combinations with the same resistance.

6. ### bwilliams60 Active Member

Nov 18, 2012
734
94
Funny, I actually figured this out as my head hit the pillow last night. I was going to retract but too tired. Good trick question for students. Love it!

7. ### MrChips Moderator

Oct 2, 2009
12,635
3,453
How about a 1 volt bulb that operates with 1 amp.

Haha, Gotcha!