Download Chapter 36 Summary – Magnetism

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Chapter 35 Summary
For current to flow in a circuit we need a complete path. This means any gaps or breaks and
all current will stop. The simplest circuit requires at least a voltage source, a resistor, and wire to
connect the circuit. An example is a flashlight which uses a battery, bulb, and metal to complete the
circuit. When we close a circuit, we are completing the path and turning it on. An open circuit
means current can’t flow and is turned off. There are 2 main types of circuits: series and parallel.
The main difference between them is that a series circuit has only one path and parallel circuits have
multiple pathways. For a series circuit, current is the same everywhere, total resistance can be found
by adding each individual resistor (this means that total resistance will be larger than any 1 resistor),
and total voltage can be found by adding the voltage drop at each resistor. The voltage source
supplies the same amount of power, so as things are added or subtracted, the power has to get split
and shared. This means devices get more or less current depending on how many ways it has to get
split and the voltage drop they get is proportional to the size of their resistance. Because the voltage
source supplies the same power, it’s cheaper to run. But with one path, everything is all on or all off.
Ohm’s Law applies for voltage, current, and resistance totals, and voltage, current, and resistance at
each resistor. For a parallel circuit, there are multiple pathways. This means that each branch gets
the same voltage as the voltage source, the total current is the sum of the current from each branch,
and the resistance will be smaller than any 1 resistor because as you add branches you add pathways
and decrease resistance. Different branches do not affect each other though and we get individual
control. This means one branch off does not change the amount of current to the others. The other
lights won’t get dimmer or turn off. This uses more power though and costs more because each
branch is supplied with power separately. If too much current flows for the size of the wire, it can
overheat, melt, and catch fire. This is called an overloaded circuit. We use fuses or breakers wired
into the circuit in series to protect this from happening. They act as a safety valve and when too
much current flows, they open the circuit and turn the whole thing off before it can burn.