Physics 2: Physical Science & Technology (PHYC10004)
Week 7
Discussion questions
1
A current-carrying solenoid is moving towards a conducting loop as shown. In what direction does the current in the loop flow when viewed as shown?
2
A long straight wire carrying a current i is in the plane of a rectangular conducting loop.
(a) What is the direction of the induced current in the rectangular loop if the current i is constant and being moved toward the rectangle?
(b) What is the direction of the induced current in the rectangular loop if the current i is increasing in the direction shown?
(c) What is the direction of the induced current in the rectangular loop if the current i is initially constant and then being shut off?
3 Suppose magnetic monopoles are discovered. What two major effects might this have on Maxwell’s four equations of electromagnetism?
Problem-solving questions
4
A circular coil consisting of 200 turns and having a radius of 0.10 metre is placed perpendicular to a uniform magnetic field of induction 0.2 T. Find the average emf induced in the coil if, in 0.1 second:
(a) the field is doubled,
(b) the field is reduced to zero,
(c) the field is reversed in direction,
(d) the coil is rotated through 90 degrees,
(e) the coil is rotated through 180 degrees.
5
The coil shown in the figure has a radius of 50 mm and comprises 100 turns of wire. The resistor has a resistance of 100 ohms.
i) A bar magnet is moved towards the coil of wire as shown in the diagram. The coil has an air core. The magnet induces an emf in the coil that causes a current to flow. Explain the direction of the current flow through the resistor shown connected across the coil.
ii) Explain the direction of the current flow if the bar magnet is now moved away from the coil.
iii) With the bar magnet held fixed, the magnetic field is measured to be 0.4 T uniformly throughout the coil. The magnetic field is then reduced linearly to zero in 5 milliseconds. Determine the voltage that now appears across the resistor. Assume the resistance of the wire is negligible compared to the value of the resistor.
6
In the figure, four long straight wires are perpendicular to the page, and form a square pattern as shown, with an edge length of 13.5 cm. Each wire carries 7.5 A; the direction in wires 1 and 4 is out of the page; the direction for wires 2 and 3 is into the page. Calculate the net magnetic force per metre of length for wire 4. Express your answer in unit vector notation
(reproduced from HRW 10th Edition, Chapter 29, Problem 37)
7
An aluminium ring oscillates vertically between point A and point B in the diagram below (point C is the midpoint of A and B). A strong, small bar magnet is fixed at point C.
(a) Sketch the variation of flux through the ring with time for one or two cycles. On your sketch show when the ring is at points A, B and C. Take t = 0 when the ring is at point A
(b) Sketch the shape of the variation of emf around the ring with time on the same set ofaxes
(c) When the ring is travelling downwards between points A and C, there is a current flowing around the ring. Identify the direction of the current flow (viewed from above), with reasons.
(Adapted from VCE Physics Examination 2013)
8
At what rate must the potential difference between the plates of a 2.0 μF parallel plate capacitor change to produce a displacement current iD of 1.5 A? (ε0 = 8.85 × 10–12 F/m)
(from HRW 10/e, Chapter 32 problem 13)
Past examination questions
9 (2004)
Explain the difference between paramagnetic, diamagnetic and ferromagnetic materials and their behaviour in a non-uniform. magnetic field. In your answer, you should include:
• A brief discussion of the magnetic nature of each type of material in terms of behaviour of the particles in the atom.
• Some discussion about the orientation of the magnetic dipole moments of atoms within a sample of each type of material in an external magnetic field.
• A description of the behaviour of a sample of these materials in a non-uniform magnetic field, clearly explaining (using diagrams) the role of the field’s non-uniformity.
10
a) In the figure, a circular loop is moved at a constant velocity through regions where uniform. magnetic fields of the same magnitude are directed into or out of the page. The field is zero everywhere else.
At which one or more of the seven indicated loop positions is the current induced in the loop:
i) Clockwise;
ii) Anti-clockwise;
iii) Zero?
b) Two diamagnetic spheres (1 & 2) are located near the south pole of a bar magnet.
i) Are the magnetic dipole moments ofthe spheres directed toward or away from the bar magnet?
ii) Are the magnetic forces on the spheres directed toward or away from the bar magnet? Explain using diagrams if necessary.
iii) Is the magnetic force on sphere 1 greater than, less than or equal to that on sphere 2?