A power and resistance puzzle
A 60 W and a 100 W bulb are connected in series.
Think about the current in the circuit, and through each bulb.
Which bulb has higher resistance? 100 W
Energy and power
The energy used by a circuit is supplied by the emf of the battery through a series of
E chem(chemical energy in the battery) → elecpotential energy of separated
charges) → K (kinetic energy of moving charges) → E (thermal energy of atoms
in the resistor)
The battery supplies power at the rate P = Iε
2 (∆V )R
The resistor dissipates power at the rateRP = IΔR = I R = R
Warming Up: What’s the voltage output of your stereo?
Suppose a stereo speaker (with a resistance of 8 Ω) uses a power of 20 watts. What is
the voltage across the speaker?
(∆V R )
PR = V 2
V = √PR
V = √8x20
V = √160
Adding Voltages in Series An electric eel may have 6,000 electrolytes connected in series. Each can produce a
voltage of 150 mV. What total voltage could the