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