Interference fringes

I was in Kota Kinabalu last week for a week long conference of 785 school principals from all over Malaysia. The highlight of the conference for me was the talk by Datuk Wira Ameer Mydin ( the Mydin shops CEO) and a most wonderful bench marking visit to SM La Salle, Kota Kinabalu.

 I was fortunate my hotel room had a window view of the sea and I watched several beautiful  sunsets through my window.

The view while being beautiful reminded me of a SPM exam question.
"What is the colour of the sky above you at sunset? 
What is the colour of the sky in front of you at sunset? 
Why do the colours of the sky differ at different positions and at different times. 
Give your explanation with the help of labelled diagrams.

Then when sunset was almost over, I drew my lace curtains and caught this view.

I wonder if this picture causes you to think of anything in Physics. Can you see wavy bright and dark lines in the sections where the curtain folds and pleats are? What do you think these wavy lines are?

They are actually interference fringes, the bright lines being constructive interference and the dark lines being the destructive interference. For interference to occur,there must be 2 coherent sources. These two coherent sources are in the top fold of the curtain and the bottom fold of the curtains. Notice you only see the light fringes where the two different curtains pleats or folds are located - one big fold near the center and one smaller fold near the side.

I remember the first time I visited Pulau Redang almost 23 years ago in 1990. During that trip, there were 2 Physics teachers among many English teachers. Suddenly we two Physics teachers saw the interference fringes on the seabed!! The white sandy sea bed was a perfect screen for interference fringes to show up. Notice the wavy fringes below the sea turtle. I wonder if you can identify the very bright points and very dark points of constructive interference and  the semi bright dark lines of destructive interference.

Suddenly there,  we two Physics teachers realized the ripple tank experiments are actually simulations of the water waves at the sea. We got so excited and jumped up and down in the sea and laughed for joy in the hot sun with the English teachers thinking we two had gone crazy.  You see, it was only then  we realized the lamp at 50 cm height above the ripple tank represent the distant sun which give parallel rays. The waves on the sea are represented by the waves we create in the ripple tank. The white screen is inspired by the white seabed.

Recently while I was in Putrajaya for the hot air balloon fiesta, I bought the giant Stinson Soap Bubble Kit and we played giant soap bubbles both in the Form 5 and Form 3 motivational slot in school. I first saw these giant soap bubbles in San Francisco . Children are always fascinated by soap bubbles whether they be big or small and in this pic, you see children running to play with the soap bubble. But do you see the colorful wavy interference fringes in the soap bubble? Interference occur because the two coherent sources are the top of the soap film and the bottom of the soap film in the bubble.

Just like the curtains, the two coherent sources are very near to each other.  This is why the distance between the two slits in the Young double slits are so close. We had fun doing the Young double slit experiment with the green laser and red laser lamps ( RMB 30/- ) I bought from Shanghai but sorry we forgot to take photos. Next time ....!

Enjoy Physics - it add beauty and wonder to life.

Hot Air Balloons fiesta in SMK Padang Tembak 2002 and in Putrajaya 2013

My students in SMK Padang Tembak had built and launched many different types of hot air balloons to understand Archimedes' principle.

When we first began, many of our hot air balloons launches failed but we learnt much from the failures. Gradually our hot air balloons rose higher. The yellow cellophane balloon launched at 12 noon ( note the short shadows) rose a little -about 5 feet above their heads.

The white mahjong paper hot air balloon launched at 10.30 am rose to about 10 feet above their heads. Our best balloons were the red cellphane balloons which they launched at about 8.00 am. This one rose swiftly above the school's highest block of 4 storeys and we released the pull back string to that balloon and it rose until until it became a little speck in the sky.

To me and my students teams, their balloon launches were fun, meaningful and memorable because they had learnt with their whole being, i.e. pyschomotor, cognitively and in the affective realm. My other tagline for learning is Hands-On, Heads-On, and Hearts-On Learning in that order. I always believe first in teaching via pyschomotor skills - through our hands, our feet as that will stimulate our thinking - our brains and finally when we see the impact of learning upon ourselves and others, the joy of learning comes in.

We spent two nights in our Cyberjaya Summerglades homes for the 5th Malaysian Hot Air Balloons fiesta on 29-31st March 2013. Since our houses were not quite furnished yet, we stayed in Andrew Seoh's house and had 7 stars service right up to the last minute of our stay. Thanks Andrew and Lydia! We never quite fully expected  what would happen in this short stay!

We woke up early to catch the hot air balloons launch in Putrajaya. Listening to the birds chirping at dawn just outside our house is just so therapeutic. We were also blessed to catch sunrise over the Putrajaya Lake just outside Summerglades.

In physics, it is necessary for the balloons to be launched early in the morning so that the  cool temperature in the morning outside the balloon is much lower compared to the hotter temperature inside the hot air  balloon. Can you see the flames heating up the air in the red Tune Talk hot air balloon? The flames make the density of the hot air inside the balloon  much lower than the density of the cold air outside the balloon in the early morning

Another thing to realize is the size of the balloon compared to the actual basket. Can you see how big the volume V of the balloon must be. If you look very closely, you can see near to my head, the small wicker basket with the captain inside it,

 Buoyant force must exceed weight for the balloon to take off.  The buoyant force can be increased by increasing the volume V and ensuring the density of the cold air outside the balloon is higher. Weight can be reduced by making the density of the air inside the balloon to be lower by heating it up. Hot air rises because it is less dense.

The best treat for me and Joanne, Lydia and Andrew was watching the balloons descend. We did not know it beforehand but the balloons had targeted to descend on the grounds near Tun Dr. Mahathir house just next to my house in Summerglades. I heard the sound of hissing gases and saw the balloons coming over Summerglades. I quickly retrieved the keys to my house. I  found Joanne also awake. Both of us watched balloons descend from my back balcony. Then we clambered over the window onto my front balcony and had a first class seat to the balloons landing. Wow! I can see again God is  the Master Conductor who orchestrated events in perfect timing and location to give zest and pleasure to His children.

Joanne strikes a classic pose on my balcony
with the Holland hot air balloon flying past us.
Lydia struck a conversation with the captain on
her balcony  while the balloon flew past Lydia.

We ran excitedly to see how and where the Holland balloon would land. We discovered it just outside the grounds of Summerglades.

We watched the captain clambered outside the wicker basket which held at least 3 big  gas tanks. She instructed her partner to quickly detach the strings from the wicker basket. Another guy ran about 100 m and to pull the main string of the balloon very strongly. This would enable the balloon to land safely on one side. About 9 men or more were involved in this tricky procedure of landing and deflating the balloon.

The  Dutch partner jumps up the wicker basket and
detach the strings. The Malaysian crew catches the string
 with the flag and hold it tight and moves it away from the balloon.

This guy ran like lightning to catch the string to
bring down the balloon.

The grey lines are the fencing in between us within Summerglades
and the  balloon outside. It takes many men to deflate the balloon

One great moment was when Captain Munic from Holland, came by and said hello to us. Joanne and Captain are all smiles as they posed for this photo with Summerglades grey fencing in between them. Captain Munic says she observed rules and did not land inside the housing areas. Joanne is smiling because we have so many unexpected happy bonuses this beautiful Easter morning.

Another bonus. We also had the pleasure to view the motorised paragliders fly around Putrajaya and over Summerglades.

One more bonus. When we returned to Andrew's house, we found he had gone out and bought roti canai telur for our breakfast. And he had viewed so many balloons landing over Summerglades in the course of buying us breakfast.God rewards you, Andrew.

When we finished our breakfast, we drove like lightning back to KL to offer praise and worship to God in TOD at Easter. Christ rose this Easter morning many years ago! Today the risen Christ has caused all our spirits and hopes to rise again as we see how He orchestrated the hot air balloons for us.  Praise God a zilliion times!