Electromagnetism

taught by Math Arena

Course description

Overview

This course is targeted at Singapore Cambridge GCE O level students, but is also relevant to IGCSE students and Singapore's Integrated program students.

What do circuit breakers and r/c car motors have in common? The answer lies in the relationship between the current that flows through a wire and its magnetic effects. Whether it's creating a field strong enough to attract a contact and break a circuit, or providing enough force to win that race, the link between electricity and magnetism is wondrous and amazing.

Course Content

You will learn:

  • How to pick the materials to use for a good electromagnet
  • How to increase or decrease the apparent weight of a wire without touching it
  • What happens to charged particles in a magnetic field
  • Some places where you might see electromagnetism being used
  • How dc motors work
  • Lots of other cool stuff!

A link to the full O level Physics syllabus can be found here

Course Prerequisites

You will need to know:

Math Arena
Math Arena

The instructor is from Math Arena.The instructor is absolutely passionate about teaching and you'll find the lessons engaging and ultimately rewarding.

Course Curriculum

Magnetic fields in coils
21:16
Q22 A long wire that carries a current I is bent into five loops as shown in the figure. If the observer could "see" the magnetic field inside this arrangement of loops, how would it appear?
Q23 A current in a solenoid creates a magnetic field. What is the effect on the magnetic field at the point P of using a larger current in the opposite direction?
Q24 In the diagram, in which direction is the magnetic field at point X?
Q25 The diagram below shows an electromagnet made from a nail, a coil of insulated wire, and a battery. The south pole of the electromagnet is located closest to point
Q26 The diagram below shows a coil of wire (solenoid) connected to a battery. The north pole of a compass placed at point P would be directed toward point
Q27 A current-carrying solenoid is placed with its axis pointing east-west. A small compass is situated near one end of the solenoid. The current in the solenoid is doubled. Which of the following best shows the new position of the compass needle?
Q28 A wire is coiled around an iron bar and connected to a 12 V battery When current flows in the wire, what are the poles attained by X, Y and Z respectively?
Q29 The diagram below shows a small magnet hanging on a thread near to the end of a solenoid carrying a steady current I. What will happen to the magnet as the iron core is inserted into the solenoid?
Q30 Two solenoids are wound on soft iron cores and connected to batteries, as shown in the diagram below. When switches S1 and S2 are closed, the solenoids
Q31 In the below, the current to both solenoids are turned on, they will________________.
Q32 Two solenoids, X and Y, are connected in series as shown and are suspended near each other. When X and Y are connected to an a.c. supply, they will
Q33 The diagram below represents a solenoid in which there is no electric current. Which one of the following best represents the magnetic field pattern due to an electric current in the solenoid?
Force on a current-carrying conductor in a magnetic field
27:00
Q39 The figure below shows an upwards force acting on a current-carrying wire. What is the direction of the magnetic field?
Q40 The diagram below shows a U-shaped wire hanging freely in rods X and Y. Rods X and Y are connected to a d.c. supply. Which of the following is true?
Q41 In the diagram below, a wire carrying an electron current into the page, as denoted by X, is placed in a magnetic field. The magnetic field exerts a force on the wire toward point____.
Q42 In the diagram at the right, when the negative current is flowing in the direction indicated by the arrow, the direction of the force in the wire will be
Q43 In the diagram below, a wire is suspended in the presence of a magnetic field. As electrons begin to flow through the wire as indicated, in which direction will the wire tend to move?
Q44 In the diagram at the right, electrons flowing through the wire as shown will cause the wire to move toward the
Q45 A wire carrying an electron current (e–) is placed between the poles of a magnet, as shown in the diagram below. Which arrow represents the direction of the magnetic force on the current?
Q46 The diagram at the right represents a conductor carrying an electron current in magnetic field B. The direction of the magnetic force on the conductor is
Q47 When the electric current in wire XY is in the direction shown, there is an upward force on the wire. If the north and south poles of the magnet exchange positions, in which direction will the force on the wire act?
Q48 A strip of aluminium foil is held between the poles of a strong magnet, as shown below. When a current is passed through the aluminium foil in the direction shown, the foil is deflected. In which direction is this deflection?
Q49 A current-carrying wire is placed between two magnets as shown below. What is the direction of force acting on the wire?
Q50 A current-carrying wire is placed between two magnets as shown below. What is the direction of force acting on the wire?
Q51 A current is made to pass through a swing mounted to the ceiling such that it can swing freely. The swing will
Q52 When the switch in the circuit shown is closed, the bare wire XY will
Force on a current-carrying conductor in a magnetic field - complex cases
22:14
Q53 Two current-carrying wires (P and Q) are placed between two magnets and their currents are equal but in opposite directions as shown below. What are the directions of forces acting on the wires?
Q54 An a.c. supply is connected to a wire stretched between the poles of a magnet. Which way will the wire move?
Q55 A copper wire is held between the poles of a magnet. The current in the wire can be reversed. The poles of the magnet can also be changed over. In how many of the four directions shown can the force act on the wire?
Q56 Four current-carrying wires are placed between two magnets as shown in the plan view below. Which wire would experience the smallest electromagnetic force?
Q57 A wire carrying a direct current is held above a magnet as shown in the diagram. The resultant magnetic field of the magnet and the wire interact with each other and the current will cause the wire to experience a force in the direction____.
Q58 In the diagram below Q is a circular coil of wire carrying a clockwise current I. P is a long, straight wire carrying a current perpendicularly into the page through the centre of the coil. Each part of Q will experience_____________________.
Q59 Four long straight parallel wires carry equal currents directed vertically out of the page. They are arranged on the corners of a square as shown in the figure below. The direction of the resultant magnetic force exerted on the wire labelled X is
Q60 The diagram shows a rectangular wire frame balanced on knife edges. One side of the wire frame rests on an electronic balance, while part of the other side lies in a magnetic field. What could be done to obtain a smaller reading on the mass balance?
Q61 A bar magnet is fixed in a container of mercury as shown. A copper wire PQ is connected to a cell and freely suspended at P. What will happen to the end Q, as seen by the observer, when the switch is closed and remains closed?
Magnetic force on particles
27:09
Q62 A magnetic force acts on an electric charge in a magnetic field when
Q63 A particle is being accelerated by a magnetic field. This particle must be
Q64 A charged particle is moving with a constant velocity. On entering a uniform magnetic field, the particle
Q65 An electron and a proton travelling with the same velocity are injected into a region of uniform magnetic field at 90° to the magnetic field direction. The initial magnetic forces on them are
Q66 A charged particle is situated in a region of space and it experiences a force only when it is in motion. It can be deduced that the region encloses _________________.
Q67 The diagram below shows electron e about to enter the region between the poles of two magnets. Upon entering the region between the poles, the moving electron will experience a magnetic force directed
Q68 Hot air from a hair-dryer contains many positively charged ions. The motion of these ions constitutes an electric current. The hot air is directed between the poles of a strong magnet, as shown. What happens to the ions? They are deflected
Q69 Upon entering the magnetic field, the negatively charged particles will be deflected
Q70 An electron traveling at a speed (V) in the plane of this paper enters a uniform magnetic field. Which diagram best represents the condition under which the electron will experience the greatest magnetic force as it enters the magnetic field?
Q71 A proton enters a region of magnetic field as shown below. The proton will
Q72 The diagram shows a beam of electrons entering a magnetic field. The direction of the field is into the page. In which direction are the electrons deflected?
Q73 The diagram shows a beam of electrons entering a magnetic field. What is the effect of the magnetic field on the electrons?