Electric Fields and Circuits

Electric Field Lines

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Electrical Potential Energy Two negatively charged balloons expel. Work has to be done to hold them together. When the balloons are released, they will move away from each other. The more charged balloons are, the more work has to be done to hold them together.

Electrical Potential Electrical potential is the electrical potential energy per charge. Electrical potential = electrical potential energy / charge 1 volt = 1 joule / 1 coulomb

Electric Potential (Voltage)

Potential Difference When there is a potential difference, charge flows. The flow of charges will continue until both ends reach a common potential. The electric current is simply the flow of electric charge.

Potential Difference

Electric Current Electric Current is a flow of electric charge. Electric charge can be carried by electrons, protons and ions. Traditionally electric current is depicted by flow of positive charge.

Resistance Resistance is defined as the ratio of potential difference to current. R = ΔV / I = constant

Resistance depends on FactorLess resistanceGreater resistance LengthshortLong Cross-sectional areabigSmall MaterialcopperAluminum temperaturelowhigh

Electric Power Electric power is the rate at which electrical energy is converted to other forms of energy. Charge moves from a terminal to the light bulbs and then back to the other terminal. Charge works for the light bulbs and its electrical potential energy decreases to zero when it moves back to the other terminal.

P = IΔV When the charge moves through the battery, the charge gains the electrical potential energy from work of the battery. ΔPE = qΔV P = ΔPE / Δt P = qΔV / Δt (We learned that current is flow of charge per second) P = IΔV

R = ΔV / I  ΔV = IR P = I(IR) = I 2 R

Let’s Practice. An electric space heater is connected across a 120 V outlet. The heater dissipates 1320 W of power in the form of light and heat. Calculate the resistance of the heater. P=IΔV 1320 = I = I 1320 = 11 2 R = 121 R 10.9 ohms = R

Let’s practice A 1050 W electric toaster operates on a household circuit of 120 V. What is the resistance of the wire that makes up the heating element of the toaster? Answer: 14 Ohms

Schematic Diagrams and Circuits

Series circuit

A B C When water passes the points A, B and C, is there any change in amount of water that passes the points in a given time? Which point has the highest water pressure, A, B or C? Which point has the lowest water pressure, A, B or C?

Parallel Circuit

Is the amount of water flowing the point A per time equal to the amount of water flowing at the point F? Is the sum of water flowing the points B, C, D and E per time equal to the amount of water flowing at the point A? A B F C D E

Is the water pressure at the point A equal to the water pressure at the point B? Is the water pressure at the point A equal to the water pressure at the point F? Which one experiences less resistance in water flowing, when there are two pipes B and C only or when there are four pipes B, C, D and E? A B F C D E