IP Topics

03 November

Water Bender

Seng Kwang Tan 13 Electric Fields, Demonstrations, IP4 10 Static Electricity

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

  1. Plastic ruler
  2. Wool
  3. Water from a tap

Procedure

  1. Turn on the faucet for the thinnest stream of water with a consistent flow.
  2. Rub the plastic ruler with the wool.
  3. 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.

02 November

Electromagnet

Seng Kwang Tan 16 Electromagnetism, Demonstrations, IP4 15 Electromagnetism

Materials

  1. Insulated wire (about 1 m in length)
  2. Iron nail (at least 5 cm in length)
  3. 1.5 V battery
  4. Adhesive tape
  5. Small metal paper clip

Procedure

  1. Test that the iron nail is not already magnetised by trying to pick up the metal paper clip with it.
  2. Strip the two ends of the wire off its insulation. Leave about 1 cm bare on each end.
  3. 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.
  4. If there is excess wire, make a second layer of coils around the first layer.
  5. Connect the ends of the wire to the terminals of the battery.
  6. Test the solenoid now by picking up the paper clip.
23 October

Electroscope

Seng Kwang Tan 13 Electric Fields, Demonstrations, IP4 10 Static Electricity

An electroscope is a device that can be used to detect or measure the amount of charge in its vicinity. One of the earliest electroscopes is the gold-leaf electroscope which was invented by a British clergyman Abraham Bennet. This is a cheaper model of the leaf electroscope made using aluminum foil.

Materials

  1. Paper clip
  2. Aluminum foil
  3. Modelling clay
  4. Glass bottle with a narrow neck
  5. Steel or brass sinker

Procedure

  1. Cut two strips of aluminum foil measuring 2 cm by 0.5 cm.
  2. Straighten the paper clip before bending both ends to make two hooks. Hang the paper clip using one hook from the sinker.
  3. Pierce each aluminum strip at one end through the other hook of the paper clip, leaving it to hang from the hook.
  4. Place the paper clip and aluminum strips inside the bottle. If the sinker is smaller than the neck of the bottle, use some modeling clay to keep it in place.
  5. Now you can test the electroscope by rubbing a comb with some wool and placing it near the paper clip.

Science Explained

Negative charges (electrons) are deposited on the comb by rubbing with wool. When the comb is placed near the sinker without touching, the negative charges in the sinker are repelled. As glass is an electric insulator, the only way for them to go is downwards onto the aluminum strips. Both strips are now negatively charged and will repel each other. The extent of their repulsion is dependent on the amount of charge on the comb and its distance from the electroscope.

22 October

Oersted’s Experiment

Seng Kwang Tan 16 Electromagnetism, Demonstrations, IP4 15 Electromagnetism

Hans Christian Oersted showed that an electric current can affect a compass needle in 1820. This confirms the direct relationship between electricity and magnetism, which in turn, paved the way for further understanding of the two. The direction of the magnetic field can be changed by flipping the wire around, which suggests that the direction of the magnetic field is dependent on the direction of current flow.

Materials

  1. 1.5V Battery
  2. Wire
  3. Compass

Procedure

  1. Place the compass on a horizontal surface.
  2. Connect the wire to both ends of the battery.
  3. Place the middle of the wire directly over the compass, parallel to the initial orientation of the needle.
  4. Observe the needle deflect to one direction.
  5. Now flip the wire over so the current flows in the opposite direction and place it over the compass again.
  6. The needle will deflect in the other direction.
  7. Additionally, you can place the compass on top of the wire now.

Science Explained

A current will carry with it its own magnetic field. The magnetic field lines form concentric circles around the wire so that the field points in one direction above the wire and the opposite direction below the wire. Using the right-hand grip rule, where one holds his hands as though he is gripping something with his thumb pointing in the direction of current flow, his fingers will curl in a way as to indicate the direction of the magnetic field. This is also the direction in which the needle deflects.

31 January

How Does Siphoning Work?

Seng Kwang Tan 04 Forces, Demonstrations, IP3 05 Density and Pressure 0 Comments

A siphon operates through the combined effects of gravity and air pressure, which work together to move liquid from a higher elevation to a lower one. Gravity is the primary force driving the flow, as it pulls the liquid from the higher container down through the siphon tube to the lower container. The liquid’s potential energy, due to its elevated position, is converted into kinetic energy as it flows downward.

Air pressure plays a crucial supporting role by maintaining the continuous flow of liquid. Atmospheric pressure on the liquid’s surface in the higher container pushes the liquid into the siphon tube. This pressure counteracts gravity’s pull that might otherwise cause the liquid to fall back into the higher container. As the liquid moves downwards, it creates a partial vacuum in the upper part of the tube, allowing atmospheric pressure to push more liquid into the tube, sustaining the flow.

Thus, a siphon can continue to operate as long as the outlet is lower than the liquid surface in the source container, the tube remains filled with liquid, and atmospheric pressure supports the flow.