Introduction
In this unit, we learned about different ways to analyze circuits. I am going to put a few important ideas in the introduction before moving on to what we covered in the unit.
- In a closed system (isolated system), there is conservation of charge, linear momentum, angular momentum, mass, and energy
- Current- Movement of charge through a conductor
Charge and Electric Force (Coulomb's Law)
Electric Charge
Electric Force
Electrostatic Induction
Objects not touching = induction
Objects touching = conduction
- An electric charge can be positive or negative
- A neutral object has an equal amount of positive and negative charges
- Elementary charge- Smallest unit of charge that can be isolated = 1.6 * 10^-19 C
- Protons are positive and electrons are negative but the magnitude is the elementary charge for both
- Variable for charge = q
- Units for charge = Coulombs (C)
Electric Force
- Opposite charges attract, like charges repel
- Coulomb's Law- The electric force increases as the charges increase, and electric force decreases as the distance between the particles increases
- The electric force is the absolute value of the charges, but use the situation to determine direction of the force
Electrostatic Induction
- Electrostatic Induction- Ability of charges in one object to affect changes in another (static electricity is an example)
- A charged object can be charged through friction or contact
- Conductors = Mobile charges (electrons can move)
- Insulators = Fixed charges (electrons can't move)
- Polarized Objects= One end is positively charged and one end is negatively charged, but the net charge is zero
- Electrons move, not protons
Objects not touching = induction
Objects touching = conduction
Electric Potential Energy and Electric Potential
- Electric Potential- Amount of energy it would take to bring an elementary charge to a specific location within an electric field
- Voltage- Measurement of the electromotive force (emf) or the difference in electric potential
- When a particle moves, the electric potential (voltage changes)
- High voltage = A particle will lose a lot of electric potential energy while moving (high potential difference)
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Here are two helpful videos on current. The first one is a brief introduction on the topic, and the second one is a video I made using a simulation in order to help explain what voltage is.
Circuits
his video does a great job of presenting voltage, current, and resistance in a way that is easy to understand. All of these elements are part of analyzing and measuring circuits.
- Series circuit- One item after another (current passes through each element)
- Parallel circuit- Different circuits connected (multiple paths)
Ohm's Law
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Current (I) = How many electrons are moving
Voltage (V) = Potential energy difference
Resistance (R) = Measurement of the difficulty for charge to flow
Voltage (V) = Potential energy difference
Resistance (R) = Measurement of the difficulty for charge to flow
Kirchhoff's Rules
- Kirchhoff's Loop Rule- Sum of all voltages is 0 (conservation of energy in a circuit)
- Think of it as a roller coaster (initial lift gets you up and then you use all of the potential energy and end up at zero at the end)
- Kirchhoff's Junction Rule- Current entering a junction = current leaving a junction (conservation of charge)
One other topic...
Electric Power = Rate at which electric potential energy is converted to heat or light
P = I ΔV = ΔV^2 / R = I^2 R
P = I ΔV = ΔV^2 / R = I^2 R
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