2Work and power of current. Joule-Lenz's law

Long-term plan unit: Electrostatics

School:

Date:

Teacher name:

Grade: 10

Number present:

absent:

Theme of the lesson

Work and power of current. Joule-Lenz's law. Current supply efficiency.

Learning objectives that are achieved at this lesson (Subject Programme reference)

Ø  To use the formulae of work, power and efficiency of current source in problem solving;

Lesson objectives

By the end of this section, students will be able to:

·         explain the concept of work and power of a current;

·         calculate the work and power of a current;

·         describe the work done by electric current;

·         explain the concept of the power and efficiency of an electrical device;

·         describe energy transformation in an electrical circuit.

Assessment criteria

Understanding

Understand  Joule-Lenz's law as the amount of heat generated in a wire;

Application

Solve problems involving Joule-Lenz's law;

Language objectives

Subject-specific vocabulary & terminology

Electromotive force (EMF)

Kirchhoff’s first law

sum of p.d.s across the resistors

sum of the e.m.f.s

loop’ in this circuit

Useful set(s) of phrases for dialogue/writing

The sum of the currents entering any point in a circuit is

equal to the sum of the currents leaving that same point.

The sum of the e.m.f.s around any loop in a circuit is equal

to the sum of the p.d.s around the loop.

Values instilled at the lesson

v  Appreciation for the unique abilities of each learner.

v  Respect for other’s opinion while working in a group.

v  Lifelong learning that theories learned from our discussion could be applied also to practical life.

v  Internationalism – the students must recognize that the discovery of capacitors is made by physicists who came from different countries.

Cross-curricular links

      Visual Literacy Instruction – the students must understand, appreciate and comprehend what they have seen in the presentation and other video materials.

      *Utilization of IT in teaching and learning process.

      Mathematics-knowledge on algebra, fundamentals and higher mathematics are pre-requisites to this lesson

ICT skills

Presentation, Interactive Board

Previous learning

The concepts of mechanical work and power;

The concepts of voltage and current; Ohm's Law.

Course of the lesson

Planned stages of the lesson

Planned activities at the lesson

Resources

Beginning

7 min

Teacher:

-Introduces the topic of day and spelling out the learning outcome they will possess after the study.

1. Organizational moment to acquaint students with the

• The theme of the lesson
• The objectives of the lesson
• The criteria of success for the lesson
• The plan of events for the lesson

2. Start. Energy transformations

Teacher shows a picture of electrical devices which transform electric energy into another one.

Matching

Presentation

Middle

8-17 min

 18-25 min

 26-30 min

 31-38 min

(W) Whole class discussion.

Energy transformation in electric circuits.

In an electric circuit, electrical energy is converted into other forms of energy. Almost always, a greater or smaller part of the energy is converted into heat (internal) energy. In heating devices, this conversion is welcomed, whereas in other devices, the resultant heat energy is usually regarded as an unwanted side effect.

Electric energy

·         The work done by electric current:

The work done by current flowing through a given element of an electrical circuit is equal to the product of the voltage across the element and the charge that has flowed through the circuit.

·         How to calculate work:

The work done by electric current in a given element of a circuit is equal to the product of the voltage across this element, the current flowing through the element and the time of flow.

(T) Teacher explanation. Joule-Lenz's law

Joule-Lenz's law shows the relationship that exists among:

·         The current that flows through a wire.

·         The heat generated by the current that flows through a wire.

·         The resistance of the wire and …

·         The time the current passes through the wire.

Joule’s law formula: Q = I² × R × t

where:

Q is the amount of heat, in Joules (J)

I is the electric current that flows through the wire, in amperes (A)

R is the value of the electrical resistance of the wire, in ohms (R)

t is the amount of time that current passes through the wire, in seconds (s).

Heating effect

Joule’s law can be established as the amount of heat (Q) generated in a wire with resistance (R), when a current (I) passes through it for a period of time (t).

This heat is directly proportional to:

·         The square of the current.

·         The resistance of wire.

·         The time the current flows through the wire.

(I) Individual work.

·         What are the heating effects caused by electric current?

Worked example

Calculate the amount of energy supplied by a 4.5 V battery when:
(a) a charge of 20 C passes through it
(b) a current of 25 mA flows through is for

      3 minutes

Solution:

Energy = potential difference x   

     Q = 4.5 x 20 = 90 J
(b) Energy = potential difference x Q =

     p.d x current x time 

Therefore:
Energy = 4.5 x 25x10-3 x 180 = 20.25 J

(f) Formative assessment.

Set of calculations for electrical energy

Presentation

Presentation

Appendix

End

  37-40 min

At the end of the lesson, learners reflect on their learning:

-           What has been learned

-           What remained unclear

-           What is necessary to work on

Where possible the learners could evaluate their own work as well as the work of their classmates using certain assess criteria.

Differentiation – how do you plan to give more support? How do you plan to challenge the more able learners?

Assessment – how are you planning to check students’ learning?

Health and safety regulations

Differentiation can be by task, by outcome, by individual support, by selection of teaching materials and resources taking into account individual abilities of learners (Theory of Multiple Intelligences by Gardner).

Differentiation can be used at any stage of the lesson keeping time management in mind.

Use this section to record the methods you will use to assess what students have learned during the lesson.

Health promoting techniques

Breaks and physical activities used.

Points from Safety rules used at this lesson.

Reflection

Were the lesson objectives/learning objectives realistic? Did all learners achieve the LO?

If not, why?

Did my planned differentiation work well?

Did I stick to timings?

What changes did I make from my plan and why?

Use the space below to reflect on your lesson. Answer the most relevant questions from the box on the left about your lesson. 

Summary evaluation

What two things went really well (consider both teaching and learning)?

1:

2:

What two things would have improved the lesson (consider both teaching and learning)?

1:

2:

What have I learned from this lesson about the class or achievements/difficulties of individuals that will inform my next lesson?