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Electric Fields and Circuits
Electric Field Lines
http://phet.colorado.edu/sims/charges-and-fields/charges-and-fields_en.html
Resistance
• Resistance is defined as the ratio of potential difference to current.
• R = ΔV / I = constant
Resistance depends onFactor Less resistance Greater resistance
Length short Long
Cross-sectional area big Small
Material copper Aluminum
temperature low high
P=I•ΔV
• R = ΔV / I ΔV = I•R• P = I•(I•R) = I2R
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
AB
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?
• 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
FC
D
E