Sharing of Teaching Experience

Title:                         Resistance

Name of School:       Hoi Ping Chamber of Commerce Secondary School

Level of Students:     S2

Topic:                      Factors affecting resistance

Subject:                   Integrated Science

Date of upload:        5/2004  

Content

(A)   Background

Time:                             70 minutes

Aim:                               To investigate the factors affecting the resistance of a wire

Previous knowledge:  Students know what resistance is and that material is a factor affecting the resistance of a wire.

Learning outcomes:     Students will be able to tell that the thickness and length of a wire will affect its resistance.

(B)   Teaching Methods

Procedure:

Introduction: (15 minutes)

Teacher recalls the students’ memory by asking the following questions.

T:     Last lesson, you’ve done an experiment to see what resistance is. Do you remember the experiment you’ve done? (Pause)

Q1.  You were given 2 different materials. What are they? (one is copper, the other is nichrome)

T:     After the experiment, we find that the brightness of the light bulb when connected to copper wire or nichrome wire is different.

Q2.   Which material results a brighter light bulb? (Copper wire)

Q3.   What is the meaning of such a result?

 * Teacher reminds students that the brightness of the light bulb is an indicator of the size of current.

 (Larger current passes through copper wire)

Q4.   So, in terms of resistance, which material has a smaller resistance, copper or nichrome? (Copper)

**If students are unable to answer Q3 and Q4, teacher can guide them with the help of the following questions:

 Q1: What can you say about the size of current if the light bulb is brighter? (the size of current is larger)

 Q2: If large current can pass through, what can you say about the resistance of the material?

   Is it high or low then? (low)

 Q3: Since copper wire results a brighter light bulb, so, does it have a high or low resistance? (low)

Teacher makes use of the blackboard to show students clearly the relation between the brightness of light bulb and the size of current and how it is related to resistance.

BLACKBOARD PLANNING

T:  From this experiment, we found that different materials have different resistance. (Teacher writes the information on the blackboard and asks students to fill in the blanks)

 *  Materials with (smaller/larger) resistance allow (larger/smaller) current to pass through.

Teacher guides students to think about the ways of controlling the size of current in a circuit. (Allow students to think. No need to answer at this moment!)

Body: ( 40 minutes)

Q1.  Are there any other factors that will affect resistance?

*Teacher asks students to look at the wires of the electrical appliances found in the laboratory, for example, air conditioner, microphone, computer, mouse, etc.

Q2.  Are there any differences in resistance between a thick wire and a thin wire?

*Teacher introduces and explains the apparatus that students would be using in checking this out.

Q3.  Besides thickness, are there any other factors affecting resistance? (Free answers)

*Teacher asks students to check out if “length” can also be a factor.

Students do experiments. Teacher walks around to assist and guide students to the fact that “thickness” and “length” of a wire affects resistance.

The following questions may help to guide the students:

For more able students:

Q1: How does the thickness of a wire affect resistance? (The thicker the wire, the smaller the resistance)

Q2: How do you know the resistance is smaller in thicker wire? (Because the bulb is brighter; the brighter the bulb, the larger the current, the smaller the resistance)

For less able students:

Q1: What happens to the brightness of the light bulb when it is connected to a thicker wire? (It is brighter)

Q2: What does it mean if the light bulb is brighter? (The size of current is larger)

Q3: If the size of current is large, how about the resistance then, is it high or low? (Low)

Q4: So, how does the thickness to a wire affect resistance? (The thicker the wire, the smaller the resistance)

(* Similar questioning technique can be used to check whether ‘length” of a wire affects resistance.)

Conclusions: (15 minutes)

Teacher checks the answers with the students and concludes that besides materials itself resistance also depends on the thickness and length of an object.

T: Now, you can answer the question that I asked you at the beginning of the lesson. How can you control the size of current in a circuit? (By changing the resistance)

  How? (Allow students to think!)

T: We shall discuss this in more detail during the next lesson.

Teacher asks students to prepare P.90-96 for the next lesson.

Reflections on the lesson:

I was satisfied with the students’ performance in this lesson. Compare with other classes, the ability of this class is rather low. They certainly have difficulties in understanding lessons conducted in English. In order to learn more effectively, they are advised to prepare their lessons before they come to class. Of course, as expected, not all students are that obedient. Sometimes they are “lazy” and do not take my advice. It is not difficult at all to tell if they have prepared their lessons or not. But this time, they were very attentive and showed great interest in answering my questions. I could see that they were really thinking hard. I knew they had done some revision. They participated actively in the experiments and also discussed with their classmates. As they were so attentive and eager to learn, they had made this lesson a success.

Science is an interesting subject. Students should be given more time to think and explore.  During lessons, if students have any difficulties, as a teacher, I think we should guide them to think more thoroughly and if we could, through questioning, lead them to find answers by themselves, instead of providing them “correct answers” immediately.

Should you have any ideas to share with me, please contact me.

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The above materials (including audiovisual materials and photographs, if any) were originated by the author. The copyright of these materials is vested in the author. The author agreed that schools or teachers might reproduce or adapt the materials with acknowledgement of the source.