Electric Charge
Atoms and Electricity
- all matter is made of atoms, which are in turn made up of protons, neutrons and
electrons - both the protons ( in the nucleus) and electrons ( outside the nucleus)
have a basic property called charge
- protons have
Magnetism From Electricity
- there is a relationship between electricity and magnetism called electromagnetism
Oersted's Discovery
- when a compass is placed near a wire carrying electricity, the compass needle
was deflected
- when the direction of the cu
Electric Circuits
- an electric circuit must be a complete closed path in order to work
Parts of a Circuit
- a source of energy, wires, a load or resistance, and a switch to control flow
- the source can be a battery, photocell o, thermocouple or generato
Electric Power
- power is the rate at which energy is produced or used
- Power (Watts) = Voltage (Volts) x Current (Amps)
- or Power (W)= Energy (Joules)
Time (second)
- a 60 W light bulb uses less energy per second than does a 100W bulb
- for larger valu
Electricity from Magnetism
- if magnetism can be produced from electricity why can't electricity be produced
from magnetism?
Electromagnetic Induction
- Farady used two coils of wire, one connected to a battery the other connected to a
galvanometers, wrap
Magnetism in Action
- when charged particles come in contact with a magnetic field a force acts on the
particle
- if the particle is moving in the same direction as the field there is no force acting
on it, so no change in its motion
- if the particle is
The Earth as a Magnet
- over time people have tried to explain why magnetic material when left free to
move always pointed in the same direction
- in 1600 a physician named Gilbert proposed that the Earth was itself a magnet
and therefore had magnetic fie
The Flow of Electricity
- current or flowing electricity requires a flow of electrons
Making Electric Charges Move
- to make anything move requires a force, and the larger the object to moved the
larger the force needed
- the larger the charge the more fo
The Nature of Magnets
Magnetic Poles
- all magnets, regardless of their shape, have two ends or poles where its magnetic
effects are the strongest
- one pole is labeled North the other is South
- magnetic forces are similar to electric forces and fields i
When two waves overlap in some region, the resulting wave is the superposition of
the waves. If this superposition pattern doesnt change for a reasonable time, then
the superposition forms an interference pattern. This pattern has points with
varying amou
The capacitance depends on K, A, k and d:
Cparallel plate = K A / (4 p k d)
where K = 1 for vacuum, A = 5 cm x 5 cm = 25 cm2 = 25 x 10-4 m2, d = 2
mm = 2 x 10-3 m, and k = 9 x 109 Nt-m2/Coul2 , so C =
[(1) * (25 x 10-4 m2) ] / [4 * 3.14 * 9 x 109 Nt-m2/Co
Besides this basic equation for power:
P = I*V
remember we also have Ohms Law:
V = I*R .
Thus we can write the following equations for power:
P = I2*R = V2/R
= I*V .
To see which one gives the most insight, we need to understand what is
being held constan
We define capacitance as the amount of charge stored per volt: C = Qstored
/ DV.
UNITS:
Farad = Coulomb / Volt
Just as the capacity of a water tower depends on the size and shape, so
the capacitance of a capacitor depends on its size and shape. Just as a
Now that we have the concept of voltage, we can use this concept to
understand electric circuits.
Just like we can use pipes to carry water, we can use wires to carry
electricity. The flow of water through pipes is caused by pressure
differences, and the
If a capacitor stores charge and carries voltage, it also stores the energy it
took to separate the charge. The formula for this is:
Estored = (1/2)QV = (1/2)CV2 ,
where in the second equation we have used the relation: C = Q/V .
Note that previously we h
For a parallel plate capacitor, we can pull charge from one plate (leaving a
-Q on that plate) and deposit it on the other plate (leaving a +Q on that
plate). Because of the charge separation, we have a voltage difference
between the plates, DV.
The harde
Using C = Q/V, we see that in series the charge moved from capacitor 2s
negative plate must be moved through the battery to capacitor 1s positive
plate.
But the positive charge on the left plate of C 1 will attract a negative charge
on the right plate, an
In this first part of the course we will consider two of the common circuit
elements:
resistor
capacitor
The resistor is an element that resists the flow of electricity.
The capacitor is an element that stores charge for use later (like a water
tower).
Cu
V=I*R, or R = rL/A
For parallel, both resistors are across the same voltage, so Vtotal = V1 = V2 .
The current can go through either resistor, so:
Itotal = (I1 + I2 ) .
Since the Is are in the denominator, we have:
R = Vtotal/Itotal = Vtotal/(I1+I2); or
1
Instead of making and storing all sizes of resistors, we can make and store
just certain values of resistors. When we need a non-standard size
resistor, we can make it by hooking two or more standard size resistors
together to make an effective resistor o