http://www.ck12.org Chapter 17. Circuits
V 1 =IR 1 = ( 0. 75 A)( 10. 0 Ω) = 7. 5 V
V 2 =IR 2 = ( 0. 75 A)( 6. 0 Ω) = 4. 5 V
Notice that the sum of the voltage drops is 12 volts.
Note that series circuits are sometimes referred to as voltage dividers. Resistors provide for different voltages in
different parts of the circuit, thus permitting for an array of voltage sources throughout the circuit.
- What is the current in each branch ofFigure17.13?
Answer:The resistors are in parallel. The voltage drop across each resistor is 12 volts. The sum of the currents in
each resistor must equal the total current, 3. 2 A(see above). The current in resistorR 1 isI 1 =RV 1. The current in
resistorR 2 isI 2 =RV 2.
I 1 =RV 1 = 1012. 0 VΩ= 1. 2 A
I 2 =RV 2 = 612. 0 VΩ= 2. 0 A
Notice that the sum of the currents is 3. 2 A.
Note that parallel circuits are sometimes referred to as current dividers. In this case, resistors can provide different
currents in different parts of the circuit.
- Are the resistors in the circuit below connected in series or parallel?
Answer: Do not be fooled by the intentionally confusing look of the circuit. The current has only one path through
both resistors. The resistors are therefore in series.
http://phet.colorado.edu/en/simulation/battery-resistor-circuit
Electrical Power
We used the term "power" earlier, when we discussed the rate at which energy is used or produced. The name for the
unit of power is watt. Perhaps you’ve seen the word "watt” on a package of incandescent light bulbs (perhaps 40-
Watt, or 60-Watt). That number indicates the power consumption of the light bulb. A 40-W light bulb, for example,
draws from the electric grid 40 Joules of energy every second.
The average power was defined earlier as the rate at which work is done, that is,