Nothing Special   »   [go: up one dir, main page]
Scribd Logo
Upload

Welcome to Scribd!

  • 0 views

    Lesson 7 Electricity and Magnetism 2nd

    Uploaded by

    Aurora Bonaobra
    Module

    Copyright:

    © All Rights Reserved
    Download as PDF, TXT or read online from Scribd

    Lesson 7 Electricity and Magnetism 2nd

    Uploaded by

    Aurora Bonaobra
    0 views2 pages
    Module

    Original Title

    Lesson-7-Electricity-and-magnetism-2nd

    Copyright

    © © All Rights Reserved

    Available Formats

    PDF, TXT or read online from Scribd

    Did you find this document useful?

    Is this content inappropriate?

    Module

    Copyright:

    © All Rights Reserved
    Download as PDF, TXT or read online from Scribd
    Download as pdf or txt
    0 views2 pages

    Lesson 7 Electricity and Magnetism 2nd

    Uploaded by

    Aurora Bonaobra
    Module

    Copyright:

    © All Rights Reserved
    Download as PDF, TXT or read online from Scribd
    Download as pdf or txt
    of 2

    SAN JOSE COMMUNITY COLLEGE

    San Jose, Malilipot, Albay

    ELECTRICITY AND MAGNETISM

    CHAPTER 2
    CURRENT ELECTRICITY
    Lesson 7

    Electrical Power and Energy

    Electrical energy makes an appliance work. The rate at which an appliance uses up electrical energy is
    called electrical power.

    Power = work
    Time

    P=W
    t

    SI unit: J or watt (W) in honor of James Watt


    s

    Recall:

    V=W ;q=W
    q V

    I =q ; q = It
    t
    Hence:
    W = It
    V
    Then:
    W = VI
    t
    Since:
    P=W
    t
    Therefore:
    P = VI

    where: P = power
    V = voltage
    I = electric current

    Other equations of power: P = I2R


    P = V2
    R

    1
    Mr. Nelson B. Bataller
    Instructor
    Sample Problems:
    1. Sixty joules of work were used to operate a certain device in 30s. How much power is used up?
    Given: W = 60J
    t = 30 s
    Required: P
    Formula: P = W
    t
    Solution: P = 60 J = 2 J = 2 W
    30 s s

    2. The electrical current through a 25 ꭥ resistance is 0.5 A. What is the power of the circuit?
    Given: R = 25 ꭥ
    I = 0.5 A
    Required: P
    Equation: P = I2R
    Solution: P = (0.5 A)2(25 ꭥ) = 6.25 W

    Electrical energy

    Electrical energy = power x time

    E = Pt

    SI unit: W.s, or kWh

    The amount of electrical energy used by an appliance depends on:


    a. Rate at which it uses energy
    b. Length of time it is being used

    Sample Problems:
    1. A 5-kW appliance was used for 1 hour. How much electrical energy was consumed?
    Given: P = 5 kW
    t=1h
    Required: E
    Equation: E = Pt
    Solution: E = 5 kW x 1 h = 5 kWh

    Answer the following:


    1. What is the difference between electrical energy and electrical power?
    2. What is the SI unit op electrical energy? electrical power?
    3. What are the factors that affect the electrical energy consumed by an appliance?
    4. A 2-kW water-heater is to be connected to a 240-V line whose circuit breaker is rated at 10 A. Will
    the breaker open when the heater is switched on? (Show your computation).
    5. A 12-V storage battery is charged by a current of 20A for 1h.
    a. How much power is required to charge the battery at his rate?
    b. How much energy has been provided during the process?
    6. What is the total amount of electrical energy consumed by three 5-W LED lights and 50-W electric
    fan if these are used for 30 days at an average of 5 hours daily?

    2
    Mr. Nelson B. Bataller
    Instructor

    You might also like