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1. Electric Power and Rating

2. Power is defined as the rate of doing work or the work/time ratio. Power has a unit of Watt which can be also expressed as Joule/ second. Power

3. When a charge is moving in a circuit, electrical energy is consumed, and is converted to other forms of energy such as heat, or light. In the process of using electrical energy, work is done on the charge. Electric Power

4. The rate at which energy is converted, or the rate at which work is done on the charge, is described as electrical power. Mathematically, electrical power is defined as: Where P is power in Watts (W), I is current in Amperes (A) and V is voltage in Volts (V). Electric Power

5. Using Ohm’s law, we can derive another expression for power: Recall: Alternative equation for power

6. An electric heater running on a 120 V source draws a current of 20 A. What is the power supplied to the heater?

7. Step 1 : Identify what is required to find in the problem. You are asked to calculate for the power (P). Step 2: Identify the given in the problem. Step 3: Write the working equation. An electric heater running on a 120 V source draws a current of 20 A. What is the power supplied to the heater?

8. Step 4 : Substitute the given values. Step 5: Find the answer An electric heater running on a 120 V source draws a current of 20 A. What is the power supplied to the heater?

9. Electricity providers measure the consumed energy per household in terms of kilowatt-hour (kWh). Kilowatt-hour defines how much energy is consumed in 1 hour, at a rate of 1000 W. To obtain a general equation for the cost (C) of running a device, we denote the rate per kilowatt-hour as r . Cost of Electrical Energy

10. The cost of running a device for a certain amount of time is: where: C is the cost in pesos P is power rating in kilowatt (kW) t is amount of time in hours (h) r is rate per kWh. Cost of Electrical Energy

11. An electric heater has a power rating of 2.40 kW. If it is being used for 3 hours a day, how much its electricity consumption? Assume that the rate of electricity consumption is 8.00 pesos/kWh.

12. Step 1 : Identify what is required to find in the problem. You are asked to compute for the cost Step 2: Identify the given in the problem. Step 3: Write the working equation. An electric heater has a power rating of 2.40 kW. If it is being used for 3 hours a day, how much its electricity consumption? Assume that the rate of electricity consumption is 8.00 pesos/kWh.

13. Step 4 : Substitute the given values. Step 5: Find the answer An electric heater has a power rating of 2.40 kW. If it is being used for 3 hours a day, how much its electricity consumption? Assume that the rate of electricity consumption is 8.00 pesos/kWh.

14. The electricity consumption cost of appliances is dependent on its power rating. The higher the power rating of a gadget or an appliance, the higher also its electricity consumption cost. 1 2

15. 500 W air conditioner, 20 W electric fan 45 W electric pot, 55 W rice cooker 95 W laptop, 180 W desktop PC Determine the appliance or gadget that has a greater electricity consumption.

16. Complete the table given below. No. Power Rating (W) Current (A) Voltage (V) 1. 100 __________________ 50 2. __________________ 5 70 3. 560 7 __________________ 4. 640 __________________ 80 5. 1080 __________________ 90

17. If you compute your electrical usage per month and its electrical consumption cost in peso, would your result correspond in your monthly electric bill? Why or why not?