Current Electricity (NA)
Upcoming SlideShare
Loading in...5
×
 

Current Electricity (NA)

on

  • 5,122 views

Key Concepts Learnt:

Key Concepts Learnt:
- conventional/electron flow
- electric circuit
- current
- voltage - potential difference, electromotive force
- resistance

Statistics

Views

Total Views
5,122
Views on SlideShare
5,107
Embed Views
15

Actions

Likes
0
Downloads
233
Comments
1

3 Embeds 15

http://mskoonworld.blogspot.com 12
http://www.mskoonworld.blogspot.com 2
http://www.slideshare.net 1

Accessibility

Categories

Upload Details

Uploaded via as Microsoft PowerPoint

Usage Rights

© All Rights Reserved

Report content

Flagged as inappropriate Flag as inappropriate
Flag as inappropriate

Select your reason for flagging this presentation as inappropriate.

Cancel
  • Full Name Full Name Comment goes here.
    Are you sure you want to
    Your message goes here
    Processing…
  • I like this for covering several concepts-pd, R, ohm's law- with my yr11
    Are you sure you want to
    Your message goes here
    Processing…
Post Comment
Edit your comment

Current Electricity (NA) Current Electricity (NA) Presentation Transcript

    • Electric current
    • Electromotive force
    • & Potential Difference
    • Resistance
    Chapter 16: Current Electricity Part I
    • state that current is a rate of flow of charge and that it is measured in amperes
    • recall the relationship charge = current x time
    • apply the relationship to new situations or to solve related problems
    Chapter 14 At the end of the chapter, you should be able to: 1. Electric Current
  • Electric Current
    • Current flow
    • Actual
    • electrons flowing from
    • -ve to +ve terminal.
    Chapter 14 Pg 241 Definition: Current is a rate of flow of charge.
    • Conventional
    • Charges flowing from
    • +ve to –ve terminal.
    Actual Conventional
  • Ampere (A) Coulomb (C) second (s) Measurement of Current Definition: Current is a rate of flow of charge. The amount of charge passing thru a given pt in 1 sec. Chapter 14 Pg 241 Time (t) Charge (Q) Current (I) SI Unit Quantity Q _______ I t Formula: I = or Q = I t Q t
  • Example 1: A current of 10 A flows through an electric heater for 10 minutes. What is the total charge circulated through the heater? [Solution] t = 10 min x 60 = 600 s I = 10 A Q = I t = 10 A x 600 s = 6000 C The total charge is 6000 C Measurement of Current Chapter 14 Q _______ I t
  • Example 2: In an electrical circuit, a charge of 60C flows past a point in 10s. What is the current in the circuit? Measurement of Current Chapter 14 [Solution] t = 10 s ; Q = 60 C Q = I t I = = 60 / 10 = 6 A The current is 6 A Q _______ I t Q t
  • Example 3: A lightning flash carries 25 C of charge and lasts for 0.01 s. What is the current? [Solution] Q = 25 C ; t = 0.01 s Q = I t 25 C = I x 0.01s 25 / 0.01 = I I = 2500A Current is 2500A Measurement of Current Chapter 14
  • Example 4: A current of 2 A is flowing through a conductor. How long does it take for 10 C of charge to pass any point? [Solution] I = 2 A ; Q = 10 C Q = I t 10C = 2A x t 10 / 2 = t t = 5 s Time taken is 5 s Measurement of Current Chapter 14
    • Ammeter
    • measures the current in a circuit
    • connects in series
    • measures in A or m A
    • has very low resistance
    There must be a closed path in order for current to flow. Ammeter Chapter 14 Pg 241 A A A +  + 
  • More common symbols can be found on pg 243 Chapter 14 Pg 243 Electric Symbols
  • Circuit Diagram Variable resistor Bulb Ammeter Voltmeter Battery Fixed resistor Switch Chapter 14 Pg 243
    • Electric current
    • Electromotive force & Potential Difference
    • Resistance
    Chapter 14: Current Electricity Chapter 14 Pg 245 Part II
    • define electromotive force (e.m.f.) as the work done by a source in driving a unit charge around a complete circuit
    • state that the potential difference (p.d.) across a circuit component is measured in volts
    At the end of the chapter, you should be able to: 2. Electromotive Force & Potential Difference Chapter 14 Pg 245
  • Electromotive Force (e.m.f) Chapter 14 Pg 245 Definition: Electromotive force is defined as the total work done by a source in driving a unit charge around a complete circuit 1 Unit charge = 1 coulomb of charge
  • Electromotive Force (e.m.f) Chapter 14 Pg 245
    • Sources of e.m.f are:
    • Electrical cells (i.e. batteries)
    • Thermocouples
    • Generators
    • etc
  • 2V Electromotive Force (e.m.f) Hi I’m Mr Coulomb (1 C) 2J of energy 2J of energy 2 J of work is done when 1 C of charge moves round the circuit Mr Coulomb goes back to the source for energy Note: 2J of electrical energy 2J of light and heat energy 2 J of energy is supplied by the cell in moving 1 C of charge round
  • Electromotive Force (e.m.f) Chapter 14 Pg 245
    • Cell
    • Source of energy
    • Produces e.m.f that pushes the charges round the circuit.
    Work done/energy is used to light up the bulb. Direction of current travel
  • Analogy The pump pushes the water to flow flow of water Work done/ energy is used to move the mill
  • Potential Difference (p.d.) Chapter 14 Pg 246 Definition: The p.d. between two points is the energy required to move 1 C of charge between them. Potential Difference (p.d.) OR Voltage (V) SI Unit : V (volts)
  • The p.d. between 2 points is the energy required to move 1 C of charge between the two points. energy E p.d. = --------------- , V = ------ or E = VQ charge Q e.g. 2V = 2 J/C Potential Difference (p.d.) Formula: E _______ V Q
  • V
    • Voltmeter
    • measures the p.d. / voltage between 2 points
    • connects in parallel across 2 points
    • measures in V or mV
    • has very high resistance
    +  +  Voltmeter Chapter 14 Pg 247 2J of energy 2J of energy
  • The diagram shows a battery with an electromotive force of 6 V in a circuit. How much energy is needed to drive 30C of charge round the circuit? E = VQ = 6V x 30C = 180 J or [Solution] Example 1 6 V
    • An electrical quantity is defined by “the energy converted by a source in driving unit charge round a complete circuit”. What is this quantity called?
    • Current B. Electromotive force
    • C. Potential difference D. Power
    Example 2 B
    • When a current of 0.5 A flows for 10 minutes through an electrical heater, 2400 J of energy is transformed.
    • Calculate the total charge moving through the heater.
    • (b) Calculate the potential difference across the heater.
    Q = I t = 0.5A x (10 x 60)s = 300 C Total charge is 300 C E = V Q 2400J = V x 300C V = 2400 / 300 = 8 V The p.d. is 8 V Example 3
    • Electric current
    • Electromotive force & Potential Difference
    • Resistance
    Chapter 14: Current Electricity Chapter 14 Pg 247 Part III
  • Chapter 14 Pg 247 The resistance is a measure of how difficult it is for an electric current to pass through a substance. Resistance
  • Chapter 14 Pg 247 Definition: The resistance of a conductor is defined as the ratio of the potential difference across the conductor to the current flowing in it. Resistance Formula: R = SI Unit : Ohms (  ) V I where R = resistance V = p.d / voltage I = current or V = IR
  • The size of the current depends on the resistance in the circuit. A A 2  5  10  With the same cell used (i.e. voltage is the same), as resistance, R increases, current, I ____________ Resistance 20 V 20 V 20 V decreases I = 10 A I = 4 A I = 2 A A
    • Resistance resists the flow of current
    • Resistance is low in conductors and very high in insulators .
    Flow of current Resistance Resistance Chapter 14 Pg 248
  • V = I R 6 = I x 4 6 / 4 = I I = 1.5 A Reading on the ammeter is 1.5 A A 4  resistor is connected in series with an ammeter and a 6 V battery, as shown. What is the reading shown on the ammeter. Example 1 R I _______ V
  • Chapter 14 Pg 249 The resistance R (= V / I) of a metallic conductor is CONSTANT under steady physical conditions Ohm's Law
  • For Ohmic conductors (Conductors that obeys Ohm’s law) e.g. pure metal Chapter 14 Pg 248 For non-Ohmic conductor e.g. filament lamp bulb I /A V/V I /A V/V Metal A Metal B I /A V/V
    • an electrical component designed to reduce the flow of current.
    • converts electrical energy to heat energy.
    • (e.g. resistors used in electric fire and filament bulb
    • convert electrical to heat and light energy)
    • represented by the symbol
    Resistor
    • Rheostat
    • a variable resistor that controls the size of a current in a circuit represented by
    Resistor
    • Procedure:
    • Set up the apparatus as shown above.
    • Adjust the variable resistor to allow the smallest possible current to flow in the circuit
    • Note the corresponding ammeter reading (I)and the voltmeter reading (V)
    • Adjust the variable resistor in steps to increase current flow in the circuit and
    • note the values of I and V for at least five sets of readings.
    • Plot a graph of V against I. The graph plotted must be a best straight line passing
    • through the origin.
    • The gradient of the best straight line obtained gives the resistance of the resistor, R.
    To determine the unknown resistance, R of a fixed resistor Pg 253 Fixed resistor A V Variable Resistor/ Rheostat
  • The unknown resistance of the resistor is found by obtaining the gradient of the straight line graph.
    • Precaution :
    • To prevent a rise in the temperature of the resistor, which may change its resistance,
    • open the circuit between readings
    • use small amount of current
    Experiment to find Resistance Chapter 14 Pg 253 I /A V/V
  • Example 2 C
  • Example 3 C
  • Example 4 B
  • Example 5 B
  • Resistivity
    • Besides physical conditions (e.g. temperature), the resistance R of a given conductor also depends on:
    • its length l
    • its cross-sectional area A
    • the type of material
  • Resistivity Formula: where R = resistance ρ = resistivity l = length A = cross-sectional area
  • Example 6
  • Example 7
  • Resistors in Series Resistors in Parallel Simulation from Crocodile Physics
  • Example 8
  • Example 9