It’s about time Singapore considered building a liquid fluoride thorium reactor as a safe source of nuclear energy. From the video, it would appear that thorium is safe as it cannot be weaponized, does not require high pressure containers and the risk of a meltdown does not exist. For a small island state like Singapore, this presents an attractive way of obtaining relatively clean abundant energy. I’m sure if we think hard enough we will be able to solve the other problems such as storage of waste products.
Perhaps the part of our syllabus on Nuclear Physics will need to be updated then.
A homopolar motor is a simple electric motor that does not require the use of a commutator. The electric current flows in a fixed direction within the wires of the motor. The following are instructions on how to construct this simple teaching tool that can be used to demonstrate how a motor works, as well as teach concepts such as Fleming’s left-hand rule and $$\mathbf{F}= I\mathbf{l \times B}$$.
Materials
Copper wire (about 22 cm)
Small neodymium magnets (1 or 2)
1.5 V AA-size battery
Base with either another magnet or a iron surface, such as the head of an iron nail
Procedure
Make a V-shaped bend in the middle of the copper wire, with about 0.5 cm on both sides of the V-shape. Bend the copper wire into a rectangular loop using the dimensions shown below.
Tip: You may use the edge of a wooden block as a guide to bend the copper wires at right angles. A pair of wooden blocks can also be used to flatten the rectangular loop if you press them together tightly with the loop in between.
Mount the neodymium magnet(s) onto the magnet or iron base.
Hook the wires at the base around the magnets.
Place the AA-sized battery with the protruding end on the magnet(s).
Complete the electric circuit by placing the V-shaped end of the rectangular loop onto the flat end of the battery and watch the loop spin.
Be careful not to keep the current flowing for too long as the battery and wire can get very hot.
Science Explained
A force acts on a current if it is placed in a magnetic field. This force is what causes the motor to spin about its axis.
To apply Fleming’s left hand rule, observe from the diagram below how the magnetic field bends around the magnet and its direction with respect to the direction of current flow. How do you think the loop will spin?
If you are having difficulty making this version of the homopolar motor, try the other design for the homopolar motor made using a screw.
A indoor boomerang can be constructed using 3 strips of cardboard put together. Throwing it may require some practice though but when you get the hang of it, it can inject great fun into your lesson. You can explore using different types of material to get the best boomerang.
Materials
Cardboard about 1 mm thick, of suitable rigidity
Staples
Scissors
Rubber band or tape for added weight
Procedure
Cardboard strip with a slit cut
Cut 3 equal rectangular strips of cardboard measuring 12 cm x 2.5 cm. You may like to trim the sharp corners on one of the ends of each strip.
Cut a slit of 1.5 cm along the middle of each strip, on the untrimmed end.
Join the strips together at the slits, the angle between two adjacent strips being 120 degrees.
3 strips of cardboard overlapping each other
One side of the slit should overlap another so that it looks like the above:
Staple the overlapping centre together.
The boomerang is ready for use! Throwing the boomerang is done by holding onto one of the wings. The boomerang should be almost vertical, at an angle of about 10o. With a flick of the wrist, spin the boomerang as it leaves the hand. The direction of spin should be toward the side that is tilted up.
Science Explained
A boomerang requires a centripetal force to cause it to fly in a circular path back to the thrower. This centripetal force comes from the lift that the wings generate as they cut through the air.
There are many ways to tune a guitar. Many musicians would have tuned a string instrument using a tuning fork at some point. However, the conventional method of tuning with a tuning fork is by listening to beats while adjusting the tension of the string. The tuning fork is of a known frequency which corresponds to a note. For instance, 440 Hz corresponds to an A-note. When the A-note string is slightly out of tune, such as having a frequency of 438 Hz, the resulting sound pattern (called beats) will have a frequency that is the difference between the two frequencies, i.e. 2 Hz. Hence, the aim of tuning by listening to beats is to adjust the tension of the string until the beats disappear.
An alternative method, which is the one we shall attempt in this demonstration, is to run the vibrating tuning fork along the E-string (this first from the top) until you reach the bridge between the 5th and 6th frets. You should expect to hear a loud resonating sound there. Otherwise, adjust the tension until you do.
All the other strings are tuned with respect to that first string.
Explanation
Resonance is the phenomenon where the frequency of the tuning fork (driving frequency) is equal to the frequency of the string (natural frequency) and maximum energy is transferred from the tuning fork to the string. The string will hence oscillate with the maximum amplitude.
A thin stream of water can be easily bent using a plastic comb or ruler which was previously rubbed with wool. This demonstrates the attractive forces between unlike charges.
Materials
Plastic ruler
Wool
Water from a tap
Procedure
Turn on the faucet for the thinnest stream of water with a consistent flow.
Rub the plastic ruler with the wool.
Place the part of the ruler which was rubbed near the stream of water without touching.
Science Explained
Water molecules are polar in nature, which means that one side (where the oxygen atoms are) is more negative while another side (where the hydrogen atom is) is more positive. When wool is rubbed with plastic, it deposits electrons on the ruler.
The electrons will remain on the plastic as it is a poor conductor of electricity. When placed near the stream of water, the water molecules reorientate themselves such that the positive pole of each molecule is now nearer to the ruler than the negative pole.
The resulting attractive forces are stronger than the repulsive forces as the forces between charges decrease when the distance apart increases.
Test that the iron nail is not already magnetised by trying to pick up the metal paper clip with it.
Strip the two ends of the wire off its insulation. Leave about 1 cm bare on each end.
Coil the wire around the iron nail, pushing each coil tightly together, to make a solenoid. Make sure you leave about 5 cm free at each end of the wire in order to connect the battery to the solenoid.
If there is excess wire, make a second layer of coils around the first layer.
Connect the ends of the wire to the terminals of the battery.
Test the solenoid now by picking up the paper clip.
