Electrical Resistance Resistance R opposition to the flow

Resistance (R) - opposition to the flow of charge, resulting in a loss of

Resistance and Resistors Some clarifications: • • Resistance is a property of a material

Resistivity The resistance of a wire is directly proportional to its length and inversely

Resistivity For any given material, the resistivity (18 -4) increases with temperature: Semiconductors are

Resistance Ohm’s Law Units: volt (V) amp (A) ohm (W)

Ohm’s Law and Resistance n Graphically – plot V vs I V Slope =

Ohm’s Law Sample Problem n Calculate the potential difference across a 150 resistor if

Power n n The rate at which a device uses energy is the power.

Electrical Power is the rate of doing work. Units:

Electrical Power in a Circuit There are several equivalent expressions for power: Unit: Watts

Sample Problem 0. 75Ω 1) A light bulb with a resistance of 0. 75Ω

Cost of Electricity n n Electric companies charge for the number of kilowatt-hours (k.

Cost of Electricity Sample Problem 2) Your electric company charges 14 ¢/k. Wh. A

Port Colborne – Electricity Prices Demand Time-of-Use Periods Price On-Peak “Time-of-Use (TOU) Prices” Mid-Peak

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Electrical Resistance

Resistance (R) - opposition to the flow of charge, resulting in a loss of potential energy. Circuit Diagram

Resistance and Resistors Some clarifications: • • Resistance is a property of a material or device. Current and charge do not get used up. Whatever charge goes in one end of a circuit comes out the other end. © 2014 Pearson Education, Inc.

Resistivity The resistance of a wire is directly proportional to its length and inversely (18 -3) proportional to its cross-sectional area: The constant ρ, the resistivity, is characteristic of the material.

18 -4 Resistivity

Resistivity For any given material, the resistivity (18 -4) increases with temperature: Semiconductors are complex materials, and may have resistivities that decrease with temperature.

Resistance Ohm’s Law Units: volt (V) amp (A) ohm (W)

Ohm’s Law and Resistance n Graphically – plot V vs I V Slope = R I

Ohm’s Law Sample Problem n Calculate the potential difference across a 150 resistor if the current that passes is 0. 27 A. (Ans: 41 V)

((12. 7) Electrical Power

Power n n The rate at which a device uses energy is the power. The faster a device uses energy, the more powerful it is.

Electrical Power is the rate of doing work. Units:

Electrical Power in a Circuit There are several equivalent expressions for power: Unit: Watts (W)

Sample Problem 0. 75Ω 1) A light bulb with a resistance of 0. 75Ω is connected to a 1. 5 V. a) Calculate the power used by the light bulb. (Ans: 3. 0 W) b) How much current passes through it? (Ans: 2. 0 A)

Cost of Electricity n n Electric companies charge for the number of kilowatt-hours (k. Wh) used. One kilowatt-hour (k. Wh) means that a kilowatt of power has been used for one hour. k. Wh is a unit of energy. 1 k. Wh = 3. 6 x 106 J

Cost of Electricity Sample Problem 2) Your electric company charges 14 ¢/k. Wh. A coffee maker has a power rating of 1 050 W. How much does it cost to use the coffee maker one hour per day for 30 days? (Ans: $4. 41)

Port Colborne – Electricity Prices Demand Time-of-Use Periods Price On-Peak “Time-of-Use (TOU) Prices” Mid-Peak Winter Season Nov to Apr 20. 80 ¢/k. Wh Weekdays: 7 a. m. to 11 a. m. 5 p. m. to 7 p. m. 14. 4 ¢/k. Wh Weekdays: 11 a. m. to 5 p. m. Off-Peak 10. 1 ¢/k. Wh Weekdays: 7 p. m. to 7 a. m. Weekends & Holidays: All Day