Download presentation

Presentation is loading. Please wait.

Published byDeonte Sullens Modified over 2 years ago

1
Topic 7: Electricity in the Home Science 9 with Mrs. M Please take off your hoods and hats Bring a calculator to class next week

2
Power Grid Topic 7

3
Power Grid The grid is a complex network that links generating stations to electric energy users (homes, factories, etc). Topic 7

4
Power Grid Topic 7

5
Transformers reduce or increase voltage of an alternating current “Step up” voltage for long-distance transmission “Step down” voltage at destination Topic 7

6
Transformers “step up” or “step down” voltage of AC current

7
Topic 7: From the Grid to Your Home Substation: Step up Transformer Residential Step down Transformer Distribution Station

8
Distribution lines -> Power meter -> Circuit breaker box Career connection: electrician, power line worker, home renovations Topic 7

9
Circuit breaker/ Main breaker Acts as a switch and safety device to cut power to the home if current is too large. Older homes have a fuse box. A fuse melts when overheated by excessive current. Prevents possible fires from overheated wires. Main breaker Topic 7

10
Branch circuits Additional circuit breakers or fuses for each branch circuit in your home Each branch supplies power to a room or electrical plug Topic 7

11
Home circuitry Topic 7

12
Wires Two live wires = neutral wire (white insulated) and hot wire (black insulated) Ground wire (bare copper or green insulation) Topic 7

13
Digital devices: machines that process numerically coded information (number codes) Binary code: on/off, 0/1 (example: switches) Transistor: electronic switch in modern devices Topic 7

14
Microprocessors contain millions of transistors https://www.youtube.com/watch?v=IcrBqCFLHIY https://www.youtube.com/watch?v=IcrBqCFLHIY

15
Measuring Electric Power Power = energy per unit of time Electric power = amount of electric energy converted to other forms (heat, light, sound, motion, etc) every second Power (in Watts) = Energy (in Joules) Time (in seconds) P = E / t Topic 7

16
Power A light bulb converts 60 J of electricity to light every second. What is the power of the bulb? P = E / t Topic 7

17
Power What is the energy produced every second in a 100 Watt light bulb? P = E / t P x t = E E = P x t Topic 7

18
We can use voltage and current to calculate Power Power (in Watts) = Current (in Amps) x Voltage (in Volts) Power = Current x Voltage P = I x V Current = Power I = P / V Voltage Voltage = PowerV = P / I Current Topic 7

19
1.36 A current passes through an electric heater plugged into a 110 V outlet. What is the power of the heater? P = I x V Topic 7

20
P = I x V Practice Problems Page 324 1. What is the power (in watts and kilowatts) of a hair dryer that requires 10 A of current to operate on a 120 V circuit? 2. The maximum current that a 68.5 cm television can withstand is 2 A. If the television is connected to a 120V circuit, how much power is the television using? Topic 7

21
P = I x V Practice Problems Page 324 3. A 900W microwave oven requires 7.5A of current to run. What is the voltage of the circuit to which the microwave is connected? 4. A flashlight using two 1.5V D-cells contains a bulb that can withstand up to 0.5A of current. What would be the maximum power of the bulb? Topic 7

22
Paying for Power Your electric company charges by kilowatt hours One kilowatt hour (kWh) is the total energy supplied to a 1000 W load during one hour of operation. Example: a hair dryer running for 1 hour that turns 1000 Joules of electrical energy to heat energy is using 1kW per hour. Topic 7

23
Cost Problem: A family uses 3000 kWh of electric energy in a two month period. If the energy costs 11 cents, what is the electric bill for that period? E = 3000 kWh Cost = 0.11$ per kWh Topic 7

24
Practice Problems Page 325 1a) You need to know conversions: 1 day = 24 hours 1 hour = 3600 seconds 30 days x 24 hours x 3600 seconds 1 day1 hour Calculate: 30 x 24 x 3600 Topic 7

25
Practice Problems Page 325 1.a) If a refrigerator requires 700W of power to function, how many kilowatt hours of power will it require in a 30 day period? b) If electricity costs 11 cents per kilowatt hour, how much would the refrigerator cost to operate in that period? Topic 7

26
Practice Problems Page 325 2. A home-owner finds that she has a total of 42 light bulbs (100 W) in use in her home. – If all of the bulbs are on for an average of 5 hours per day, how many kilowatt hours of electricity will be consumed in a 30 day period? – At 11 cents per kilowatt hour, how much will operating these lights cost the home-owner during that period? – How much money would the home-owner save if she switched all of the bulbs to energy-saving 52 W light bulbs? Topic 7

27
Practice Problems Page 325 3. Bob has a stereo that operates at 120 V, using 2.5 A. – How much power does Bob’s stereo need to operate? (Hint: Think back to the previous power- calculation) – If Bob plays his stereo for an average of 5 hours each day, how much electricity will he use in a 30 day period? Topic 7

28
Power Rating You can buy 60 W, 100 W, or 120 W light bulbs The power is stamped on the product “EnerGuide” labels help consumers decide what to buy Topic 7

29
Electrical Devices and Efficiency No device is 100% efficient Efficiency = useful energy output x 100% total energy input Recall P = E/t E = P x t Energy is the power multiplied by time the device is on Topic 7

30
Light Bulbs Incandescent bulbs 5% efficient most of the energy is converted to heat Halogen bulbs are 15% efficient waste heat can be a fire hazard halogens can last 2 to 6x longer than incandescent Fluorescent tubes 20% efficient last 13x longer than incandescent Topic 7

31
What is the Efficiency? 1000 W electric kettle takes 4 min to boil. The energy used is 1.96x10^5 J (196000 J). P = 1000 W t = 4min x 60sec/min = 2400seconds E = P x t Efficiency = useful energy output x 100% total energy input Topic 7

32
Practice Problems Page 329 Find the efficiency of a 23W fluorescent tube that is used 4.0 hours per day and in that time produces 6.624x10^4 J of useful light energy. A 100W incandescent bulb also produces about 6.624x10^4 J over a 4.0 hour period. What is the efficiency of this bulb? Based on your answers to questions 1 and 2, how much money would you save in a 30-day month if you replaced 25 of the 100W incandescent bulbs with 23 W fluorescent bulbs? Assume that the bulbs operate 4 hours a day, and that electricity costs 11 cents per kilowatt hour.

33
Home Electrical Safety Electric shock = current flowing through the body Short circuit = when electricity transfers on unintended path. It happens when bare wires touch directly and current flows between them Topic 7

34
Home Electrical Safety Don’t overload power outlets Topic 7

35
Home Electrical Safety Never change a light-bulb or clean devices that are still plugged in Water + electricity = bad news Topic 7

36
Electric Safety Outdoors Don’t go swimming in a lightning storm Topic 7

37
Electric Safety Outdoors Don’t touch live wires or power lines Don’t dig up underground utility wires Topic 7

38
REVIEW P = I x V is the formula on your PAT Be able to manipulate it for: – I = P/V – V = P/I

Similar presentations

OK

Using Energy Wisely Section 12.2. Your Hydro (Energy) Bill.

Using Energy Wisely Section 12.2. Your Hydro (Energy) Bill.

© 2017 SlidePlayer.com Inc.

All rights reserved.

Ads by Google

Led based message display ppt on tv Ppt on political parties and electoral process of japan Ppt on areas related to circles class 10th Ppt on id ego superego in lord Ppt on bing search engine Ppt on drugs and medicines Ppt on outside activities for preschoolers Importance of water for kids ppt on batteries Miracles in the bible ppt on how to treat Ppt on satellite orbiting