Presentation is loading. Please wait.

Presentation is loading. Please wait.

Thermodynamic temperature

Similar presentations


Presentation on theme: "Thermodynamic temperature"— Presentation transcript:

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.


Download ppt "Thermodynamic temperature"

Similar presentations


Ads by Google