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Depth of Liquid in a Cup

16/04/2020 at 7:34 am (last edited 04/01/2021 at 3:11 pm)

Describe how a force is exerted on a current-carrying conductor that is cutting through the magnetic field of a magnet.

30/03/2020 at 12:29 pm (last edited 15/07/2020 at 12:44 pm)

When a current flows through the current-carrying conductor, a magnetic field forms around the current-carrying conductor.

The interactions between the magnetic fields of the current-carrying conductor and the magnet produce regions of unequal magnetic field densities around the conductor.

A force will be exerted on the conductor, moving it towards the region of lower magnetic field density.

Why must the fuse/switch/circuit breaker be connected to the live wire?

1092 admin

25/03/2020 at 3:35 pm (last edited 15/07/2020 at 12:51 pm)

The live wire is at high voltage, and carries the current from the electrical mains to the electrical appliance. If any electric fault occurs, resulting in high current flow, the fuse/switch/circuit breaker on the live wire will immediately cut off the high current/high voltage before the high current/voltage can cause damage to the electrical wirings and the appliance.

Different Routes

1088 admin

24/03/2020 at 6:17 pm (last edited 01/02/2021 at 1:25 pm)

A student wishes to walk from the corner X to the corner Y through streets as given in the street map as shown below.
He does not move to the left or downwards.
(i) Find the number of different routes from X to Y the student can take.
(ii) The student wishes to visit P on his way from X to Y as indicated in the diagram below. Find the number of different routes he can take.

OABC is a tetrahedron

1081 admin

23/03/2020 at 6:57 pm (last edited 08/02/2021 at 7:58 am)

Explain why calcium oxide has a higher melting point than potassium fluoride.

1078 admin

18/03/2020 at 9:32 am (last edited 16/07/2020 at 8:40 am)

The charges of Ca²⁺ ions and O^2- ions in CaO is higher than that of K⁺ ions and F^– ions in KF. The higher the ionic charge, the higher the electrostatic force of attraction between the oppositely charged ions, so more energy is required to overcome the electrostatic force in CaO than in KF.

Hence, CaO would have a higher melting point than KF.

What is the potential hazard when the switch of an electrical appliance is connected to the neutral wire instead of the live wire?

1074 admin

17/03/2020 at 9:12 am (last edited 15/07/2020 at 12:55 pm)

The live wire is at high potential difference, while the neutral wire is at zero potential difference. When the switch is turned off, the electrical appliance will still be at high voltage, since the electrical appliance is still connected to the electrical mains via the live wire.

The electrical appliance being ‘live’ even though the switch is turned off is potentially hazardous as it increases the risk of electrocution and overheating and electric fire if a path to a lower potential difference is established.