More Kirchoffs Rules

1
More Kirchoffs Rules
We have three unknowns, so we have to find three
equations to arrive at a solution.
Lets find the currents I1, I2 and I3 using the
rules we discussed last time.
2
More Kirchoffs Rules
When we go around the loops, we have to get the
signs right. Think about water flowing. If we
go with the flow through a resistor we go
downhill and use a minus sign. If we go through
a resistor against the flow we go uphill and use
a plus sign. For batteries use a plus sign going
from - to and vice versa.
Now that we have used the current rule, we still
need two more equations, so well have to do two
voltage loops.
3
More Kirchoffs Rules
4
More Kirchoffs Rules
We now have our three equations in three unknowns
to solve.
5
More Kirchoffs Rules
6
Charging Batteries
7
Capacitors in Parallel Circuits
We want to find the equivalent capacitor that
will store the same charge.
8
Capacitors in Series Circuits
We want to find the equivalent capacitor that
will store the same charge.
9
Resistor Capacitor Circuits
RC has units of time and is called the time
constant.
10
Resistor Capacitor Circuits
11
Blinker for your Children
12
Heart Pacemaker
Substitute a persons heart for the gas-filled
bulb.
13
Electrical Hazards

• You can feel 0.001 ampere (1 milliampere)
• 0.005 amperes hurts
• 0.010 amperes causes muscle spasms
• 0.015 amperes loss of muscle control
• 0.070 amperes disrupts heart rhythms (fatal)
• Over 1 ampere stops the heart

14
Electrical Meters

• A galvanometer is a device that measures
  electrical current
• It works based on magnetism which we will study
  soon
• Currents in wires produce magnetism
• We can make something move in a way proportional
  to the amount of current

15
Electrical Ammeters
The resistor adjusts the scale readings on the
ammeter. A small current sill send the
galvanometer full-scale. Decide how much current
to pass through the meter vs. how much goes
through the resistor to adjust.
16
Electrical Voltmeters
We have to calculate, based on the maximum
full-scale current reading, what we want the
maximum voltage scale reading to be. Then we
place a series resistor in place to make the
galvanometer read full scale for the current that
would result from that full-scale voltage.