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New Senior Secondary Physics Compulsory: Electricity and Magnetism Chapter 4 Electromagnetism Page 1 CHAPTER 4 ELECTROMAGNETISM 1 Magnetic Charge and Permanent Magnet Concept of Magnetic Charge Permanent Magnet 2 Magnetic Field Definition of magnetic field Magnetic Field of the Earth

CHAPTER 4 ELECTROMAGNETISM Magnetic Charge · PDF fileNew Senior Secondary Physics Compulsory: Electricity and Magnetism Chapter 4 Electromagnetism Page 1 CHAPTER 4 ELECTROMAGNETISM

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Page 1: CHAPTER 4 ELECTROMAGNETISM Magnetic Charge · PDF fileNew Senior Secondary Physics Compulsory: Electricity and Magnetism Chapter 4 Electromagnetism Page 1 CHAPTER 4 ELECTROMAGNETISM

New Senior Secondary Physics Compulsory: Electricity and Magnetism Chapter 4 Electromagnetism

Page 1

CHAPTER 4 ELECTROMAGNETISM

1 Magnetic Charge and Permanent Magnet

Concept of Magnetic Charge

Permanent Magnet

2 Magnetic Field

Definition of magnetic field

Magnetic Field of the Earth

Page 2: CHAPTER 4 ELECTROMAGNETISM Magnetic Charge · PDF fileNew Senior Secondary Physics Compulsory: Electricity and Magnetism Chapter 4 Electromagnetism Page 1 CHAPTER 4 ELECTROMAGNETISM

New Senior Secondary Physics Compulsory: Electricity and Magnetism Chapter 4 Electromagnetism

Page 2

Magnetic Field Pattern Draw the electric field patterns around the following configurations.

3 Electromagnetism: Moving Charge → Magnetic Field

Moving Charge Generates Magnetic Field: (Direction: Right Hand Grip Rule) Long Straight Wire Circular Coil

Solenoid

Page 3: CHAPTER 4 ELECTROMAGNETISM Magnetic Charge · PDF fileNew Senior Secondary Physics Compulsory: Electricity and Magnetism Chapter 4 Electromagnetism Page 1 CHAPTER 4 ELECTROMAGNETISM

New Senior Secondary Physics Compulsory: Electricity and Magnetism Chapter 4 Electromagnetism

Page 3

Moving Charge Generates Magnetic Field: (Magnitude) [FX only] Long Straight Wire Circular Coil

Solenoid

Electromagnets Three ways to increase the strength of an electromagnet: 1.

2.

3.

Page 4: CHAPTER 4 ELECTROMAGNETISM Magnetic Charge · PDF fileNew Senior Secondary Physics Compulsory: Electricity and Magnetism Chapter 4 Electromagnetism Page 1 CHAPTER 4 ELECTROMAGNETISM

New Senior Secondary Physics Compulsory: Electricity and Magnetism Chapter 4 Electromagnetism

Page 4

[HKCEE] Which of the following diagrams shows the magnetic field pattern formed around a flat circular current-carrying coil, in the plane as shown above?

[HKCEE] A small compass is placed near a long current carrying wire. In which of the following diagrams is the compass needle pointing in the correct direction? (1) Compass above the wire (2) Compass below the wire (3) Current flowing out of paper A. (1) only B. (2) only C. (1) and (3) only D. (2) and (3) only E. (1), (2) and (3)

[HKCEE] The diagram above shows a simple electromagnet. Which of the following can increase the strength of the electromagnet? (1) Decreasing the resistance of the variable resistor (2) Replacing the soft iron core with one made of steel (3) Replacing the battery with a 50 Hz a.c. source A. (1) only B. (3) only C. (1) and (2) only D. (2) and (3) only E. (1), (2) and (3)

Page 5: CHAPTER 4 ELECTROMAGNETISM Magnetic Charge · PDF fileNew Senior Secondary Physics Compulsory: Electricity and Magnetism Chapter 4 Electromagnetism Page 1 CHAPTER 4 ELECTROMAGNETISM

New Senior Secondary Physics Compulsory: Electricity and Magnetism Chapter 4 Electromagnetism

Page 5

[HKALE] [FX only]

The above figure shows two long parallel straight wires separated by a distance of 0.2 m, carrying currents of 1 A in opposite directions. The magnitude field at a point X mid-way between the wires is (Given : permeability constant μo = 4π x 10-7 TmA-1) A. 0 T B. 2 x 10-6 T into paper C. 2 x 10-6 T out of paper D. 4 x 10-6 T into paper E. 4 x 10-6 T out of paper

[HKALE] [FX only] Two parallel straight conductors separated by a distance r carry currents in the same direction. Which of the following statements is/are correct? 1) The two wires attract each other. 2) The force acting on each wire is inversely proportional to r2. 3) The wires produce a magnetic field with maximum flux density midway between them. A. (1), (2) and (3) B. (1) and (2) only C. (2) and (3) only D. (1) only E. (3) only

Page 6: CHAPTER 4 ELECTROMAGNETISM Magnetic Charge · PDF fileNew Senior Secondary Physics Compulsory: Electricity and Magnetism Chapter 4 Electromagnetism Page 1 CHAPTER 4 ELECTROMAGNETISM

New Senior Secondary Physics CompulsoryChapter 4 Electromagnetism

Page 6

Applications 1. Electric Bell

2. Telephone

Compulsory: Electricity and Magnetism

Page 7: CHAPTER 4 ELECTROMAGNETISM Magnetic Charge · PDF fileNew Senior Secondary Physics Compulsory: Electricity and Magnetism Chapter 4 Electromagnetism Page 1 CHAPTER 4 ELECTROMAGNETISM

New Senior Secondary Physics Compulsory: Electricity and Magnetism Chapter 4 Electromagnetism

Page 7

4 Electromagnetism: Magnetic Field → Moving Charge

Moving Charge Experience Force in Magnetic Field: (Direction: Fleming’s Left Hand Rule)

[HKCEE] The above diagram shows three long straight wires X, Y and Z. X and Y carry currents flowing into the paper while Z carries a current flowing out of the paper. The currents are all equal in magnitude. What is the direction of the resultant force acting on X? A. P B. Q C. R D. S E. T

[HKCEE]

In the figure, a copper rod is suspended horizontally by two insulating threads AB and CD, and the direction of the magnetic field is into the paper. What happens when the switch of the circuit is closed? A. The copper rod will move into the paper. B. The copper rod will move out of the paper C. The copper rod will swing into and out of the paper alternately. D. The tension in each thread is decreased. E. The tension in each thread is increased.

Page 8: CHAPTER 4 ELECTROMAGNETISM Magnetic Charge · PDF fileNew Senior Secondary Physics Compulsory: Electricity and Magnetism Chapter 4 Electromagnetism Page 1 CHAPTER 4 ELECTROMAGNETISM

New Senior Secondary Physics Compulsory: Electricity and Magnetism Chapter 4 Electromagnetism

Page 8

Turning Effect on Coil: Motor

[HKCEE]

The figure above shows a rectangular loop of wire carrying a steady current I. The rectangular loop can rotate freely about PQ. If a uniform magnetic field to the right is applied, which of the following is correct? Resultant magnetic field Rotation of the rectangular loop about PQ acting on the rectangular loop A. non-zero clockwise B. non-zero anti-clockwise C. zero clockwise D. zero anti-clockwise

Page 9: CHAPTER 4 ELECTROMAGNETISM Magnetic Charge · PDF fileNew Senior Secondary Physics Compulsory: Electricity and Magnetism Chapter 4 Electromagnetism Page 1 CHAPTER 4 ELECTROMAGNETISM

New Senior Secondary Physics Compulsory: Electricity and Magnetism Chapter 4 Electromagnetism

Page 9

Simple D.C. Motor

Simple A.C. Motor

Factors Affecting Turning Effects on Motor 1.

2.

3.

4.

Page 10: CHAPTER 4 ELECTROMAGNETISM Magnetic Charge · PDF fileNew Senior Secondary Physics Compulsory: Electricity and Magnetism Chapter 4 Electromagnetism Page 1 CHAPTER 4 ELECTROMAGNETISM

New Senior Secondary Physics Compulsory: Electricity and Magnetism Chapter 4 Electromagnetism

Page 10

Moving Charge Experience Force in Magnetic Field: (Magnitude: Lorentz Force Law) [FX only]

Current Experience Force in Magnetic Field: (Magnitude: Lorentz Force Law) [FX only]

[HKALE] [FX only] A moving-coil galvanometer with a coil of area A and N turns has a full-scale deflection for a current I. If the coil were of area 3A and 2N turns, the current which would give full scale deflection would be A. I/6 B. 2I/3 C. I D. 3I/2 E. 6I

Page 11: CHAPTER 4 ELECTROMAGNETISM Magnetic Charge · PDF fileNew Senior Secondary Physics Compulsory: Electricity and Magnetism Chapter 4 Electromagnetism Page 1 CHAPTER 4 ELECTROMAGNETISM

New Senior Secondary Physics Compulsory: Electricity and Magnetism Chapter 4 Electromagnetism

Page 11

[HKALE] [FX only] [Cyclotron]

A particle, of mass 3.2 x10-26 kg and charge -1.6 x 10-19 C, enters a uniform magnetic field of flux density 0.08 T at a speed of 105 ms-1, as shown. It will A. Pass undeflected through the magnetic field. B. Be deflected upward in a circular arc of radius 0.25 m. C. Be deflected upward in a circular arc of radius 0.50 m. D. Be deflected downward in a circular arc of radius 0.25 m. E. Be deflected downward in a circular arc of radius 0.50 m.

Page 12: CHAPTER 4 ELECTROMAGNETISM Magnetic Charge · PDF fileNew Senior Secondary Physics Compulsory: Electricity and Magnetism Chapter 4 Electromagnetism Page 1 CHAPTER 4 ELECTROMAGNETISM

New Senior Secondary Physics Compulsory: Electricity and Magnetism Chapter 4 Electromagnetism

Page 12

5 Drift Velocity [FX only]

Drift Velocity [FX only]

[HKALE] [FX only] A p.d. of 10 V is applied across a uniform wire of resistance 5.0Ω . The number of conduction electrons per unit volume of the wire is 1.0 x 1028 m-3 and its cross-sectional area is 1.0 mm2. What is the average drift velocity of conduction electrons in the wire? (Given : charge on electron = -1.6 x 10-19 C)

[HKALE] [FX only] A resistance wire is connected across the terminals of a battery. Which of the following statements is INCORRECT? A. Before connection to the battery, the conduction electrons in the wire move randomly. B. After connection to the battery, an electric field is set up along the length of the wire. C. The conduction electrons in the wire are accelerated momentarily in the opposite direction to that of the electric field. D. The conduction electrons collide with one another, giving out heat energy. E. The current in the wire is proportional to the average drift velocity of the electrons.

Page 13: CHAPTER 4 ELECTROMAGNETISM Magnetic Charge · PDF fileNew Senior Secondary Physics Compulsory: Electricity and Magnetism Chapter 4 Electromagnetism Page 1 CHAPTER 4 ELECTROMAGNETISM

New Senior Secondary Physics CompulsoryChapter 4 Electromagnetism

Page 13

6 Hall Effect [FX only]

Hall Effect [FX only]

Derivation of Hall Voltage [FX only]

Compulsory: Electricity and Magnetism

Derivation of Hall Voltage [FX only]

Page 14: CHAPTER 4 ELECTROMAGNETISM Magnetic Charge · PDF fileNew Senior Secondary Physics Compulsory: Electricity and Magnetism Chapter 4 Electromagnetism Page 1 CHAPTER 4 ELECTROMAGNETISM

New Senior Secondary Physics Compulsory: Electricity and Magnetism Chapter 4 Electromagnetism

Page 14

Importance of Hall Effect [FX only] 1. Reveal the nature of charge carrier

2. Hall Probe

[HKALE] [FX only] In the Hall probe, the slice of semiconductor inside has 2510 charge-carriers per cubic metre. When a steady current of 0.4 A passes through the slice and a uniform magnetic field of 0.1 T applies perpendicular to it, a Hall voltage of 20 μV is set up. Find the thickness of the slice. (Given : electronic charge = 1.6 x 10-19 C)

Page 15: CHAPTER 4 ELECTROMAGNETISM Magnetic Charge · PDF fileNew Senior Secondary Physics Compulsory: Electricity and Magnetism Chapter 4 Electromagnetism Page 1 CHAPTER 4 ELECTROMAGNETISM

New Senior Secondary Physics Compulsory: Electricity and Magnetism Chapter 4 Electromagnetism

Page 15

[HKALE] [FX only]

The figure shows the essential parts of an apparatus to determine the Hall effect. Which of the following statements is/are correct? 1) In the arrangement above, the Hall p.d. is developed across PQ. 2) The magnitude of the Hall potential is greater if the applied magnetic flux density is increased. 3) The magnitude of the Hall potential is less if the width PQ of the specimen is decreased. A. (1), (2) and (3) B. (1) and (2) only C. (2) and (3) only D. (1) only E. (3) only

[HKALE] [FX only] The figure shows a semiconductor specimen containing negative charge carriers. It has a constant current flowing to the right and is perpendicular to a uniform magnetic field pointing out of the paper. Which of the following is/are correct for the Hall voltage developed between the upper and the lower faces of the specimen? 1) The Hall voltage will be reversed if the specimen is replaced by another semiconductor containing positive charge carriers. 2) The Hall voltage will become larger if the specimen is replaced by a metallic specimen of the same dimensions and carriers the same amount. 3) The Hall voltage will become smaller if the separation t between the upper and lower faces is reduced while the current is kept uncharged. A. (1) only B. (3) only C. (1) and (2) only D. (2) and (3) only

Page 16: CHAPTER 4 ELECTROMAGNETISM Magnetic Charge · PDF fileNew Senior Secondary Physics Compulsory: Electricity and Magnetism Chapter 4 Electromagnetism Page 1 CHAPTER 4 ELECTROMAGNETISM

New Senior Secondary Physics Compulsory: Electricity and Magnetism Chapter 4 Electromagnetism

Page 16

FINAL REMARKS

The study of magnetism shows a strong parallelism with electrostatics. Firstly, magnetic charges and fields are much like electric charges and their corresponding electric fields, with the only exception that magnetic charges always occurs in pairs, constituting the smallest magnetic unit to be magnetic dipole.

Apart from generating magnetic fields by magnetic charges, it is even more important to observe that moving electric charges also generate and feel magnetic field. This is a strong linkage of electricity and magnetism as we can see that magnetism is just the ‘moving’ version of electrostatics. This connection of electricity and magnetism is fundamentally related to relativity, which is a theory of relative motion.