How I Teach ... Get classes moving on convection

13th September 2013 at 01:00
Lava lamps and newspaper pages bring the topic to life

"It's that time of year again, isn't it?" my daughter says as I surreptitiously steal her lava lamp.

Sometimes in science, you just have to observe and think. How often do your students get the chance to do this? How often are they given the freedom to discuss a concept?

My students enter the darkened lab with the lava lamp placed centre stage and cool jazz playing in the background (perhaps some Miles Davis). In silence, I gesture for them to sit down on prearranged stools while I continue to stare at the lamp. Given confidence and trust, they eventually relax and do the same.

How long they will do this for depends, of course, on the class - I've got to 20 minutes on occasions. After a suitable time, I break the silence and say: "What questions do you think I will ask?"

I give them time to think of ideas: Why are we doing this? How does this work? What's happening here? What is this called? What is the lamp made of?

Eventually, I steer the conversation around to convection and give them a brief explanation of the word in terms of expansion and changing density. I then split them into groups, give them an A3 sheet of paper and ask them to think of and sketch other examples of convection currents - for example, those in the Earth's mantle, causing the tectonic plates to move; hot-air balloons; wind and sea breezes; pizza ovens; hot-water heating; kettles.

I circulate during the task: this is when most of the "teaching" is done. I get the students to exchange their sheets of paper and try to fill in the gaps in each other's examples. I follow this discussion with the usual convection demonstrations - for example, using a convection tube.

Now, I test the students' understanding using a "What if .?" scenario, issuing groups (or individuals) with blank newspaper front pages bearing the headline "Convection stops". The scenario is that all convection currents have suddenly ceased, and students have to consider the consequences to everyday life and the long-term survival of the human race.

The page is divided into sections with titles, such as "Our kitchen correspondent reports", "Our science correspondent contemplates the long- term effects" and so on. Getting students to fill in the blanks is a perfect way to assess their grasp of the topic and helps with preparing follow-up activities.

I like to give students a choice of homework tasks. One option is to ask them to explain convection to their imaginary eight-year-old cousin, using 50 words or less. This is a great way of evaluating their understanding and is quick and easy to mark (my first criterion for a homework task).

Alternatively, I ask students to plan an investigation into lava lamps. What would the variables be? How would you make it a fair test?

By the way, what is the similarity between a lava lamp and most Premier League footballers? They are both interesting to watch, but not very bright.

Simon Porter teachers physics for Nord Anglia Education. His "What if ." newspaper resource can be found on TES Connect at bit.lyWhatIfFrontPage

10 ways to circulate understanding

1. Boiled down
By the end of this lesson, your students should be experts in the movement of heat through a liquid. If they aren't, get them to make you cups of tea until it sinks in.

2. Convection confusion
Clear up misconceptions about convection with this presentation explaining the process. It has molecules with smiley faces - what more could you ask for?

3. Feeling hot
This differentiated activity sheet includes questions such as "Why are houses in warmer climates a different colour from those in the UK?". The answer is not down to personal taste.

4. Radiator reason
This worksheet requires students to colour in the molecules moving away from and towards a radiator according to how hot they are - blue for cold and red for warm.

5. Watch and learn
This video enables students to visualise the convection process with the help of two glasses of liquid containing red and blue spheres, representing hot and cold currents.

6. Annotation anarchy
In this activity, students have to complete and annotate diagrams. Get it wrong and all hell could break loose as the imaginary molecules are forced to defy the rules of nature.

7. Convection quiz
While it may not have the big-bucks monetary appeal of a game show such as Who Wants To Be a Millionaire?, this challenging convection quiz will soon bring out students' competitive instincts - and all the while they will be increasing their knowledge of the subject.

8. Brilliant baking
Teach convection by investigating how baking scones on different shelves in the oven affects the result - a tasty and enlightening lesson.

9. Practical points
This worksheet gives students practical examples of convection at work, including balloon flight.

10. Turn up the heat
Test your students' knowledge by pitting them against one another as they take on this extensive and informative quiz.


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