Dạy học môn Vật Lý bằng tiếng Anh

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EDUCATION AND TRAINING DEPARTMENT OF TRA VINH PROVINCE

<b>NGUYEN THIEN THANH HIGH SCHOOL FOR THE GIFTED</b>

<b>PHYSICAL LECTURE</b>

<b> </b>

<b>LECTURER</b>

<b> MS. Viên Tuấn Anh</b>

<b>Tra Vinh city, 2016</b>

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<b>CHAPTER 2 </b>

<b>STEADY CURRENT</b>

◦

<b>_{UNIT 7.}</b>

<b>_{STEADY CURRENT}</b>

◦

<b>_{UNIT 8.}</b>

<b>_{ELECTRICAL ENERGY. ELECTRICAL POWER}</b>

◦

<b>_{UNIT 9.}</b>

<b>_{OHM’S LAW FOR THE ENTIRE CIRCUIT}</b>

◦

<b>_{UNIT 10.}</b>

<b>_{COMBINING POWER SUPPLIES INTO AN ADAPTER}</b>

◦

<b>_{UNIT 11.}</b>

<b>_{HOW TO SOLVE SOME PROBLEMS ABOUT THE}</b>

<b>ENTIRE CURCUIT</b>

◦

<b>_{UNIT 12.}</b>

<b>_{PRACTICE: DETERMINING THE ELECTROMOTIVE}</b>

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<b>UNIT 8. </b>

<b>ELECTRICAL ENERGY. ELECTRICAL POWER</b>

<b>I – ELECTRIC ENERGY CONSUMPTION </b>

<b>AND ELECTRICAL POWER</b>

<b>II – POWER OF HEAT OF A CONDUCTOR </b>

<b>WHEN AN ELECTRIC CURRENT PASSES </b>

<b>THROUGH IT</b>

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<b>1. Electric energy consumption of a circuit</b>

<b>I – ELECTRIC ENERGY CONSUMPTION AND </b>

<b>ELECTRICAL POWER</b>

<b>+</b>

U

<b></b>

-R

I

Figure 8.1

<b>A = Uq = UIt (8.1)</b>

<b>A : electric energy consumption of a circuit (J) </b>

<b>U : potential difference (V)</b>

<b>q : electrical charge (C)</b>

<b>I : current Intensity (A)</b>

<b>t : time (s) </b>

<i><b>The amount of electric energy that a circuit consumes when a current passes </b></i>

<i><b>through to transform into other energy forms, is measured by the work of </b></i>

<i><b>electric force when shifting charges in direction.</b></i>

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<b>2. Electrical power</b>

<b>I – ELECTRIC ENERGY CONSUMPTION AND </b>

<b>ELECTRICAL POWER</b>

<b>P : electric power (W)</b>

<b>A : electric energy consumption of a circuit (J) </b>

<b>U : potential difference (V)</b>

<b>I : current Intensity (A)</b>

<b>t : time (s) </b>

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.

<b>C4. Tell units of the quantities in the formula (8.2)</b>

A

UI

(8.2)

t





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<b>1. Joule – Lentz’s law</b>

<b>II – POWER OF HEAT OF A CONDUCTOR WHEN </b>

<b>AN ELECTRIC CURRENT PASSES THROUGH IT</b>

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.

<b>C5. Prove that the power of heat in a conductor when an </b>

<b>electric current passes through it is calculated by the formula</b>

<b>And tell the measument units of the quantities in the formula </b>

<b>above. </b>

2

Q RI t



(8.3)

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<b>2. Power of heat in a conductor when an electric current passes </b>

<b>through it</b>

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.

<b>II – POWER OF HEAT OF A CONDUCTOR WHEN </b>

<b>AN ELECTRIC CURRENT PASSES THROUGH IT</b>

2

Q

RI

(8.4)

t

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<b>1. Work of a power supply</b>

<b>III – WORK AND POWER OF A POWER SUPPLY</b>

<i>Power consumption in the entire circuit is equal to the work of strange force in the </i>

power supply. From the formula , we have the formula to calculate the

work A

_ng

of the power supply

<b>2. Power of a power supply</b>

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

I

(8.6)

t

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<b>SUMMARIZE MAIN CONTENT</b>

◦

_{1. Power consumption of a circuit:}

◦

_{2. Power of a circuit:}

◦

_{3. Joule-Lenzt’s law:}

◦

_{4. Power of heat of a conductor:}

◦

_{5. The work of power supply:}

◦

_{6. The power of the power supply:}

A = Uq = UIt (8.1)

A

UI

(8.2)

t

P





2

Q RI t



(8.3)

2

Q

RI

(8.4)

t

P





ng

A

  

q

It

(8.5)

ng

ng

A

I

(8.6)

t

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Exercise 1

<b>Electric consumption is measured with:</b>

<b>Results</b>

A. A Voltmeter

B. An electricity meter

C. An ammeter

D. An electrometer

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Exercise 2

<b>Which of the following units is electric power measured in?</b>

<b>Results</b>

A. Joule (J)

B. Watt (W)

C. Newton (N)

D. Coulomb (C)

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Exercise 3

<b>Calculate electricity energy consumption and electric </b>

<b>power when an electric current with the intensity of 1 A </b>

<b>passes through the conductor for 1 hour, given that the </b>

<b>potential difference between two ends of this </b>

<b>conductor is 6V.</b>

Solution:

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Exercise 4

<b>On the label of an electric kettle, </b>

<b>there are values of 220 V – 1000 W.</b>

<b>Solution</b>

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

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Exercise 5

<b>A power supply has the electromotive power of </b>

<b>12 V</b>

<b>. When we connect this </b>

<b>power supply with a light bulb to make a closed circuit, it supplies an electric </b>

<b>current with the intensity of </b>

<b>0.8 A</b>

<b>. Calculate the work of this power supply </b>

<b>which has been produced in for </b>

<b>15 minutes</b>

<b> and calculate the power of the </b>

<b>power supply at that time.</b>

Solution:

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Exercise 6

<b>Name an electric device or equipment for each </b>

<b>of the following cases</b>

<b>Results</b>

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

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Choose the true answer.

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