Electricity & Magnetism Unit 2 Electricity & Magnetism

Expected Performances D4. Explain the relationship among voltage, current and resistance in a simple series circuit. D5. Explain how electricity is used to produce heat and light in incandescent bulbs and heating elements. D6. Describe the relationship between current and magnetism.

Electricity Electricity: energy due to the movement of electrons through a material. Discovered by Ben Franklin.  

Two types of electricity Static electricity: electricity involving a build-up of stationary charges. Current electricity: electricity involving the flow of e- through a material.

Static Electricity The accumulation of excess electrical charge on an object. To create static electricity electrons are transferred between materials, by friction/rubbing causing one material to build up an excess of electrons, while a second material ends up with a shortage of electrons.

- charge = material with excess of electrons + charge= material with shortage of electrons If these charges become large enough the electrons jump from – to + creating a spark (lightning)

Law of charges: Like charges repel, unlike charges attract. “Likes repel. Opposites attract.”

Law of Conservation of Charge Electrical events simply rearrange the charges (move them from one object to another object, but the total charge remains constant)

Charged objects are surrounded by an electrical field that is similar to magnetic fields. Electrical Field – Area around a charged object where its affects can be noticed.

Static charges are not noticed until something interacts with their field or they move by: 1. Conduction: a material that can carry e- that comes in contact with a charged object resulting in an electron flow (static discharge).

2. Induction: an object’s e- shift due to the presence of an electric field

Ohm’s Law Voltage, current and resistance are all related to each other by a formula called Ohm’s Law, developed by George Simon Ohm in 1827. Current = Volts/ Resistance I= V/R

Current Current: rate at which e- move past a point in a wire. Unit: ampere (amp or A)

Voltage Voltage: the difference in electrical potential between two points. Unit: Volts (V) Voltage provides the force that causes e- to flow through a circuit. An increase in voltage causes an increase in electron flow.

VT = V1 + V2 + V3

Resistance Resistance - opposition of a substance to a flow of electrons. Unit: Ohms Ω The higher the resistance; the lower the current.

Factors Affecting Resistance Material   Thickness of a wire Length of a wire Temperature

Power Power: The rate at which energy is transferred or used in an electrical circuit. Unit: Watts (W)

Steps to solving Word Problems: Read the problem 2. List all known values with their units 3. Write out equation with unknown isolated 4. Plug in #’s with units 5. Solve, give answer with PROPER UNIT!

Formulas Current = Volts/ Resistance I= V/R Power is a function of Voltage and current expressed by the equation. P = V x I

Sample Problem #1 What is the current passing through a 3 W resistance that is connected to a 12 volt battery?

Sample Problem #2 A 30 amp current is passing through a 4 W resistor, what is the voltage in the circuit?

Sample Problem # 3 A 6 v battery pushes electrons through a circuit with a current of 0.3 amps, what is the resistance of this circuit?

What is the resistance of the bulb? Sample Problem #4 How much current passes through a 40 W bulb attached to a 120 v power source? What is the resistance of the bulb?

A 100 W bulb has a 0.2 amp current passing through it. Sample Problem #5 A 100 W bulb has a 0.2 amp current passing through it. What is the resistance of the bulb?