|
Hi Gibbsy.. the following is an attempt of demystification...
A car battery output is at 12v. The little PP3 battery pack in the fire alarm is 9v. Sticking two of these together can produce 18V . .. obviously bigger than 12V.
A car battery can easily put 10 Amps into a car headlight and therefore a power level of 12V *10 A of 120 Watts of power..and do this for a number of hours.
Our two PP3s ,produce 18V but cannot drive more than 100mA even into a short circuit. ..so connecting a car headlamp would not even make it glow red.
We say the car battery has an internal resistance of maybe 1/20 ohm and our PP3 of probably 100 ohms.
When a voltage is applied to a circuit containing a resistance ,a current will flow and power will be consumed ,both in the resistance and also in any internal resistance inside the voltage source. The power in the resistance is P = V*I .the voltage difference across the resistance times the current flowing in the resistance . However because current depends on the voltage, there are a few math relationships we can swop around ...
power is also V^2/R or power is I^2 *R
. Unfortunately the headphone manufacturers keep rearranging the deckchairs,and quote power which is a useless measure. Since they have already decided on the size of resistance in their phones, what they should say is ..This phone needs X volts to generate Y dBs ,and never exceed Z volts , |
|