Dạy học môn Vật Lý bằng tiếng Anh

Power of heat P in a conductor when an electric current passes through it is specific to the speed of heat radiation of that conductor and is specified by radiated heat [r]

EDUCATION AND TRAINING DEPARTMENT OF TRA VINH PROVINCE

NGUYEN THIEN THANH HIGH SCHOOL FOR THE GIFTED

PHYSICAL LECTURE

LECTURER

MS Viên Tuấn Anh

Tra Vinh city, 2016

ELECTRICITY - ELECTROMAGNETISM

GEOMETRICAL OPTICS

CHAPTER 2

STEADY CURRENT

◦ UNIT 7. STEADY CURRENT

◦ UNIT 8. ELECTRICAL ENERGY ELECTRICAL POWER

◦ UNIT 9. OHM’S LAW FOR THE ENTIRE CIRCUIT

◦ UNIT 10. COMBINING POWER SUPPLIES INTO AN ADAPTER

◦ UNIT 11. HOW TO SOLVE SOME PROBLEMS ABOUT THE

ENTIRE CURCUIT

◦ UNIT 12. PRACTICE: DETERMINING THE ELECTROMOTIVE

UNIT 8

ELECTRICAL ENERGY ELECTRICAL POWER

I – ELECTRIC ENERGY CONSUMPTION

AND ELECTRICAL POWER

II – POWER OF HEAT OF A CONDUCTOR

WHEN AN ELECTRIC CURRENT PASSES

THROUGH IT

III – WORK AND POWER OF A POWER

SUPPLY

1 Electric energy consumption of a circuit

I – ELECTRIC ENERGY CONSUMPTION AND ELECTRICAL POWER

-R I Figure 8.1

A = Uq = UIt (8.1)

A : electric energy consumption of a circuit (J)

U : potential difference (V)

q : electrical charge (C)

I : current Intensity (A)

t : time (s)

The amount of electric energy that a circuit consumes when a current passes through to transform into other energy forms, is measured by the work of electric force when shifting charges in direction.

C1 Tell units of the quantities in the formula (8.1) C2 State the effects that an electric current can cause C3 What tool is used to measure electric energy consumption? What’s the value of each measument

of that tool (in joule)

2 Electrical power

I – ELECTRIC ENERGY CONSUMPTION AND ELECTRICAL POWER

P : electric power (W)

A : electric energy consumption of a circuit (J)

U : potential difference (V)

I : current Intensity (A)

t : time (s)

Power of a circuit is the consumed power of electric energy of that circuit and has a value equal to electrical energy that circuit consumes in a unit of time, or equal to the product of the voltage between two ends of the circuit and current passing through that circuit.

C4 Tell units of the quantities in the formula (8.2)

A

t

P

1 Joule – Lentz’s law

II – POWER OF HEAT OF A CONDUCTOR WHEN

AN ELECTRIC CURRENT PASSES THROUGH IT

where Q : thermal energy (J)

The thermal energy radiating in a conductor is directly proportional to the resistance of the conductor, with the square of current nad with the time that

an electric current passes through that conductor.

C5 Prove that the power of heat in a conductor when an electric current passes through it is calculated by the formula

And tell the measument units of the quantities in the formula above

2

Q RI t  (8.3)

2 2

2 Power of heat in a conductor when an electric current passes through it

Power of heat P in a conductor when an electric current passes through it is specific to the speed of heat radiation of that conductor and is specified by radiated heat in that conductor in a unit of time.

II – POWER OF HEAT OF A CONDUCTOR WHEN

AN ELECTRIC CURRENT PASSES THROUGH IT

2

Q

t

P  

1 Work of a power supply

III – WORK AND POWER OF A POWER SUPPLY

Power consumption in the entire circuit is equal to the work of strange force in the

power supply From the formula , we have the formula to calculate the work A ng of the power supply

2 Power of a power supply

The power of a power supply is specific to the speed of work performance of that power supply and is specified by the work of the power supply in a unit of time This power P ng is also equal to electric consumption power of the entire circuit.

ng

A    q It (8.5)

A (7.3) q

 

ng ng

A

t

P  

SUMMARIZE MAIN CONTENT

A = Uq = UIt (8.1) A

t

P  

2

Q RI t  (8.3)

2

Q

t

P  

ng

A    q It (8.5)

ng ng

A

t

Exercise 1

Electric consumption is measured with: Results

A A Voltmeter

B An electricity meter

C An ammeter

D An electrometer Choose the true sentence

Exercise 2

Which of the following units is electric power measured in? Results

A Joule (J)

B Watt (W)

C Newton (N)

D Coulomb (C) Choose the true answer.

Exercise 3

Calculate electricity energy consumption and electric power when an electric current with the intensity of 1 A passes through the conductor for 1 hour, given that the potential difference between two ends of this conductor is 6V.

Solution:

A = ξIt = 6.1.3600 = 21600 J

Exercise 4

On the label of an electric kettle, there are values of 220 V – 1000 W Solution

a) Tell the meaning of numbers obove

b) Use an electric kettle with the voltage of 220 V to boil 2 litres of water from the temperature of 25 0 C

Calculate the time of boiling water, known that the efficiency of the kettle

is 90% and the heat capacity of water

is 4190 (J/(kgK))

+ 220 V : rated level voltage + 1000 W : rated level power

+ Thermal energy: Q = UIt = Pt + Water absorbed a thermal energy:

Q a = mcΔt = D.V.c.(t 2 – t 1 ) = 1.2.4190.(100 – 25) = 628500 J and, Q a = 0,9Q = 0,9UIt

→t ≈ 698,33 (s)

Exercise 5

A power supply has the electromotive power of 12 V When we connect this power supply with a light bulb to make a closed circuit, it supplies an electric current with the intensity of 0.8 A Calculate the work of this power supply which has been produced in for 15 minutes and calculate the power of the power supply at that time.

Solution:

A = ξIt = 12.0,8.15.60 = 8640 J

P = ξI = 12.0,8 = 9,6 W

Exercise 6

Name an electric device or equipment for each

a) When operating, it transforms electrical energy

into thermal energy and light energy

b) When operating, it transforms the whole

electrical energy into thermal energy

c) When operating, it transforms electrical energy

into mechanical energy and thermal energy

d) When operating, it transforms electrical energy

into chemical energy and thermal energy

Bulb

Electric Cooker

Fan

Electrolytic tank

Top 10 Ways To Save Electricity at Home

Choose the true answer.

THANK YOU FOR ATTENDANCE