hello forum,
just a simple question about power dissipation and resistors:
If a conductor has infinite conductivity (zero resistivity) then the voltage across it is zero, so by the formula P= I^2 R, it dissipates zero power as heat. Imagine connecting wires.
but if I use the formula P=V^2/R, would I get an indeterminate form: 0/0 since V=0 and R=0 ?
In a simple circuit, if the load is meant to generate a lot of heat (for heating or cooking) , do we want the wires to be very conducting and dissipate almost no heat (small wire gauge), but do we want the load resistor to be large or small?
IF the voltage is constant, it appears that we would need a small load resistor R_L, according to the I^2 R, so more current goes out ( and current is at the 2nd power).If the resistance were too big, little current would go out, and little power dissipated.
It seems that the more the resistance, the less the ohmic loss... something wrong here..
If two resistors are in series (same current) then the bigger resistor dissipates more heat. If they are in parallel, the smaller resistor makes more heat.
In the case of a fixed voltage, I guess we want to match the heater resistor to the internal resistor of the voltage source. That gives maximum power transfer and therefore dissipation.
But what if, in some "ideal" case, I had perfectly conducting wires and a perfect battery ( no internal resistance). Would I choose a large or a small resistance for the heater in order to generate the max heat? The voltage would be all across the resistor, no matter if it is small or large. The smaller the resistor the higher the current, the more power.
But there is a threshold. How small can the resistance be ?
If there resistance is too small, then no power is dissipated across it, since there is voltage drop either...
thanks
antennaboy
just a simple question about power dissipation and resistors:
If a conductor has infinite conductivity (zero resistivity) then the voltage across it is zero, so by the formula P= I^2 R, it dissipates zero power as heat. Imagine connecting wires.
but if I use the formula P=V^2/R, would I get an indeterminate form: 0/0 since V=0 and R=0 ?
In a simple circuit, if the load is meant to generate a lot of heat (for heating or cooking) , do we want the wires to be very conducting and dissipate almost no heat (small wire gauge), but do we want the load resistor to be large or small?
IF the voltage is constant, it appears that we would need a small load resistor R_L, according to the I^2 R, so more current goes out ( and current is at the 2nd power).If the resistance were too big, little current would go out, and little power dissipated.
It seems that the more the resistance, the less the ohmic loss... something wrong here..
If two resistors are in series (same current) then the bigger resistor dissipates more heat. If they are in parallel, the smaller resistor makes more heat.
In the case of a fixed voltage, I guess we want to match the heater resistor to the internal resistor of the voltage source. That gives maximum power transfer and therefore dissipation.
But what if, in some "ideal" case, I had perfectly conducting wires and a perfect battery ( no internal resistance). Would I choose a large or a small resistance for the heater in order to generate the max heat? The voltage would be all across the resistor, no matter if it is small or large. The smaller the resistor the higher the current, the more power.
But there is a threshold. How small can the resistance be ?
If there resistance is too small, then no power is dissipated across it, since there is voltage drop either...
thanks
antennaboy