Download presentation
Presentation is loading. Please wait.
1
Thermodynamic temperature
SI and Prefix Engineers communicate using standard language of measurement: International System of Units (SI) adopted in 1960 Basic Units Quantity Basic unit Symbol Length meter m Mass kilogram Kg Time second s Electric current ampere A Thermodynamic temperature kelvin K Luminous intensity candela cd
2
SI and Prefix Engineers communicate using standard language of measurement: International System of Units (SI) adopted in 1960 These are derived from basic units Derived Units
3
Charge, Current and Voltage
Charge – the most basic quantity of electric circuit – measured in Coulomb (C) Elements of an atom : electrons, protons and neutron negative charge positive charge neutral 1 electron carries x C of (negative) charge i.e. - 1 C consist of 1/(1.602 x ) of electrons = 6.24 x electrons
4
Charge, Current and Voltage
When electrons move in an electric circuit, they cause the Current to flow i Direction of electron flow Direction of current flow = movement of positive charge Current : time rate of change of (positive) charge Mathematically, , measured in amperes (A)
5
Charge, Current and Voltage
- Charge transferred between to and t e.g. 1 A = 1 coulomb of charge flows in 1 second i (A) 1 q (C) t (s) 1 1 t (s)
6
Charge, Current and Voltage
t (s) q (C) 1 2 t (s) q (C) i (A) i (A) 1 -1 t (s) t (s)
7
Charge, Current and Voltage
Two common types of current flow t (s) i (A) Direct current - DC - constant with time t (s) i (A) Alternating current - AC - varies sinusoidally with time we will discuss more on this later in the course
8
Charge, Current and Voltage
Voltage (potential difference) between two points, being equal to the electrical energy gained by a unit positive electric charge moving from one point to the other. Voltage: The amount of energy needed to move a unit positive electric charge from one point to the other - measured in volts (V) Mathematically, 1 V = 1 J/C
9
Charge, Current and Voltage
Voltage (potential difference) between two points, being equal to the electrical energy gained by a unit positive electric charge moving from one point to the other. a b + Vab Vab : Electrical energy gained by a unit positive charge when it moves from b to a “Point a is at potential of Vab higher than point b” “Potential at point a with respect to point b is Vab” As a unit charge moves from a to b it looses electrical energy. Where does the energy go ?
10
Charge, Current and Voltage
- 10 V + a b + 10 V a b “Point a is at potential of 10 V higher than point b” “Point a is at potential of -10 V lower than point b” “Point b is at potential of 10 V lower than point a” “Point b is at potential of -10 V higher than point a”
11
Charge, Current and Voltage
Two common types of voltage t (s) v (V) DC Voltage - constant with time t (s) v (V) AC Voltage - varies sinusoidally with time
12
Power and energy is related mathematically :
Power an Energy Power and energy is related mathematically : p = power, w= energy :: the time rate of expanding or absorbing energy :: power is measured in watts (W)
13
Use the Passive Sign Convention when calculating power:
Power an Energy Power of an element is the product of voltage across it and the current through it Use the Passive Sign Convention when calculating power: + v i i + v p= vi p= -vi Absorbing power Supplying power
14
Power an Energy Using passive sign convention, power can either be positive or negative ABSORBED SUPPLIED Examples Using passive sign convention, + 3 V 2 A Power absorbed , p = 2 x 3 = 6 W
15
Power an Energy Using passive sign convention, power can either be positive or negative ABSORBED SUPPLIED Examples Using passive sign convention, + 3 V - 4 A Power absorbed , p = -4 x 3 = -12 W OR, Power supplied , p = 12 W
16
Power an Energy Using passive sign convention, power can either be positive or negative ABSORBED SUPPLIED Examples Using passive sign convention, 6 V + - 4 A Power supplied , p = 6 x -4 = -24 W OR, Power absorbed , p = 24 W
17
Power an Energy Using passive sign convention, power can either be positive or negative ABSORBED SUPPLIED Examples Using passive sign convention, 6 V + - 4 A Power absorbed , p = 6 x -4 = -24 W OR, Power supplied , p = 24 W
18
Power an Energy Using passive sign convention, power can either be positive or negative ABSORBED SUPPLIED Examples Using passive sign convention, -6 V + - 4 A Power absorbed , p = -6 x -4 = 24 W
19
Sums of power absorbed and supplied in a circuit always equal to ZERO
Power an Energy For any electric circuit , Sums of power absorbed and supplied in a circuit always equal to ZERO
20
Power an Energy We paid bill to TNB based on the amount of electric energy we consumed – energy is measured in Joules (J) Since , energy absorbed or supplied by an element from to t to to is : Unit for energy used by TNB is Wh or kWh (1 Wh = ???? J)
21
Power an Energy The amount of electric energy consumed depends on power ratings of the electric devices we use: e.g. a 100W bulb consumed 100 x 60 x 60 = 360, 000 J of energy in 1 hour OR 0.1 kWh of energy.
Similar presentations
© 2024 SlidePlayer.com Inc.
All rights reserved.