MCAT (PHYSICS)

positive charges and negative charges (electrostatics)

field points out (POS)

filed points in (NEG)

What is a Field

Trait that creates an Area of influence (force)

Only influences things with the same trait.

Field Lines

Never cross or overlap

Closer they are = stronger

Farther = weaker

Coulomb’s Law

Need two charges to have a force.

Gravity and Coulomb are twins.. (mass + gravity constant instead)

Electric Field Charge

You only need one charge to have a field.

given EFC:

f = qE

Vector

Magnitude + Direction

Tip to tail

Multiple charges? Add their force as vectors

Net force = Vector sum

Electric Potential Energy

U = qV (given voltage)

E =V/D

Voltage

V = kq/r

J/C units..

Electric potential no energy

V = E*D

The FUEV matrix

Photoelectric effect

E of photon = hf

work function is the energy to free it = greek letter

NEW TOPIC

Magnetic Field

An area of influence

Trait: moving charges (charge + velocity)

• The field goes from North to South

• N - N S - S repel

• S - N - attract

• Angle between V and B

Curly Right Hand Rule

The magnetic field being produced.

• Field around a current

Variables: Moving charge (V) and direction (B)

Down - Counter Clockwise Ring

Up - Clockwise Ring

Dot = Towards

X = Away

Direction of Mag Field - Fingers

Current Direction - Thumb

Straight (open) Right Hand Rule

Force on a charge

Direction of Mag Field - Fingers

Current Direction - Thumb

Direction of force - Palm of Hand

If palm is towards you = the force is out of the page and a dot. (+)

If palm isn’t facing you = the force is in the page and an x. (-)

No force if V and B are parallel

When negative.. do as positive then flip

NEW TOPIC

Circuits

Circuits are anything that have to do with electricity.

Current = Charge/Time (I = q/t)

Unit = Amp (A)

Current is always in opp direction of electron flow

Battery provides voltage.

How to utilize electricity = resistance

Ohms Law : V = IR

Ohm’s Law

V = IR

If voltage goes up, current goes up.

Resistance does not depend on voltage or current

Resistance

R = p*L / A

Bigger area? Resistance decreases.

Bigger length? Resistance increases.

Series

Series: One path, current is the same everywhere, goes through each resistor.

More length. More resistance.

Req = R1 + R2

Parallel

Parallel: Extra lanes, the current can go in the resistor it wants. More area. Resistance decreases.

1/req = 1/R + 1/R2

Don’t forget to do the reciprocal

I1 + I2 (Branch Current)

Loop Rule

Voltage drops when met with a resistor.

When the voltage is back to the battery it should be 0. To go through the resistors voltage will drop.

You need some voltage to pass through each resistor in a series.

Current in resistors would be

Power

P = IV (current * voltage)

No voltage? P = I²*R

No current? P = V²/R

USE PIV AS BASE.

Ammeter vs voltmeter

Ammeter wired in series

Ideal internal resistance low

Voltmeter wired in parallel

Ideal internal resistance high