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Difference between current

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juan123

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I have seen different voltages on a power supply on computers. I have seen that in some there is 5volts and -5volts. Whats the difference??? also, what does a transistor do?
 
The 5 and -5 volts that you saw on the pwr supply in a computer is the same as +5 and -5, just like the - and + that you will see on any battery.

A transistor is the building block of almost any electronic device. There are three leads on a transistor: The collector, base, and emitter. If there is an electrical signal at the base, then the transistor will let electricity flow through the other two leads, collector and emitter. There are different kinds of transistors, but this is the most common, a bjt. Say that you put a light sensor at the base of the transistor, you could control a buzzer, or whatever, based on the amount of light that falls upon the light sensor.

Hope this helped :D If it didn't, just hollar!
 
The 5 and -5 volts that you saw on the pwr supply in a computer is the same as +5 and -5, just like the - and + that you will see on any battery.

Nice! :D If I may add another point. As you may know, voltages are normally measured in respect to ground (0 Volts). So, +5 volts means that there is a potential difference of 5 volts, which is positively charged. The same goes for -5 volts conversely. NOW, this does not mean that the potential difference between +5 and -5 volts is 5 volts. Rather, the potential difference is 10 volts. Remember, ground is the middle ground (no pun :D ) here. You can think of +5 volts being measured 5 inches away from a center point (ground). AND -5 volts is measured 5 inches in the opposite way from the same center point. Thus, if you measure the distance between your measurements (+5 & -5), you'll get 10 inches. I'm sure you get the idea.
 
I've heard of this, but I never really got it. Does it make any difference whether you connect to 0 volts, or -whatever? I kind of missed the fundamentals in my studies :oops:
 
zachtheterrible said:
I've heard of this, but I never really got it. Does it make any difference whether you connect to 0 volts, or -whatever? I kind of missed the fundamentals in my studies :oops:

It depends entirely what you are doing, when taking voltage measurements it's usual to measure from the 0V point, so (depending on the circuit) you may have both positive and negative voltages. Another option is to measure from the negative rail, sometimes this makes it easier to understand what is happening. Even more occasionally you may measure from the positive rail, but this is fairly unusual.

When connecting different circuits together you need to be aware of their power supply requirements, 'usually' you would connect their 0V rails together - but there are exceptions, it depends on the exact circumstances.
 
I know that ground would be between the negative n positive of two batteries if they were hooked up to a circuit. Where would the ground be if you only had one battery?
 
In a simple circuit, using only one battery, the '+' terminal would be +v (probably 9v) and the '-' terminal would be 0v which would be ground.
 
a +/-5V supply w.r.t. the local 0V is also 5V and 10V if you re-reference w.r.t. -5V

Remember "Voltage across a component" and "Current through a component"

The voltage across a component is dependant on the direction of the current through it.
 
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