PH 1120
Electricity and Magnetism
P.K.Aravind
Term B05
STUDY GUIDE #3
In this part of the course we will study the following topics:
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Current, resistance and resistivity
Electromotive force, energy and power in simple electrical circuits
Analysis of multiloop DC circuits using Kirchoff’s Rules
Force on a charge or current element in a magnetic field
Objective 13: Current and resistance
(a) Understand electric current, current density and drift velocity and their interrelationship.
(b) Understand resistance, resistivity and conductivity and their interrelationship. Know how to
calculate the resistance of a sample whose resistivity and geometric dimensions are given.
Suggested Study Procedure for Objective 13:
Read Ch.25-1 for Obj 13(a). You should understand the difference between the drift velocity of a
charge carrier (which is small) and its actual velocity (which is large). Read Ch.25-2,3 for
Obj 13(b), but you can skip over the part concerning the temperature dependence of resistivity.
Study Examples 25.1 and 2. Examples 25.3 and 4 are optional reading for advanced students.
Suggested Problems for Objective 13:
Problems 25-1,3,5,10,13,14,17,53,62.
Objective 14: Simple DC circuits
(a) Understand the terms emf, internal resistance, terminal voltage and load resistance as they apply
to a battery or other source of potential difference.
(b) Know how to calculate the power dissipated in a resistor carrying a known current.
(c) Know how to calculate the equivalent resistance of a set of resistors in a series or parallel
configuration or in a combination of these configurations.
Suggested Study Procedure for Objective 14:
Read Ch.25-4 for Obj 14(a) and study all the worked examples in this section.
Read Ch.25-5 for Obj 14(b) and study all the worked examples in this section.
Read Ch.26-1 for Obj 14(c) and study both the worked examples in this section.
Suggested Problems for Objective 14:
Problems 25-29,31,32,33,36,38,42 and 26-5,12,15.
Objective 15: Kirchoff’s Rules and multiloop DC circuits
Know how to apply Kirchoff’s rules (the junction and loop rules) to solve multiloop circuit
problems.
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Suggested Study Procedure for Objective 15:
Read Ch.26-2 and study all the worked examples in this section. You should also study Example
26.14 “A kitchen circuit” on p.1006. Ch.26-5 on Power Distribution Systems is optional reading,
but is highly recommended.
Suggested problems for Objective 15:
Problems 26-19,24,57,63,67.
Objective 16: Magnetic Forces
(a) Know how to calculate the cross (or vector) product of two vectors using the right hand rule.
Also know how to calculate the cross product of two vectors in i,j,k notation.
(b) Know how to calculate the force on a charged particle in a magnetic field.
(c) Know how to calculate the force on a current carrying wire in a magnetic field.
Suggested Study Procedure for Objective 16:
Read Ch.1-10 for Obj 16(a) and study all three worked examples (the first two are concerned with
the scalar product and the third with the vector product). Read Ch.27-1,2 for Obj 16(b). Read
Ch.27-6 for Obj 16(c); the main results you need to know are Eqns.(27.19,20), which are illustrated
in the two worked examples at the end of this section.
Suggested Problems for Objective 16:
Problems 27-1,5,7,53,64,65,67,71,74.
For all Mastering Physics homework assignments, go to www.masteringphysics.com,log
in, click on “assignment list” and select the assignment number listed for that homework. You will
get 4 chances to submit the correct answer. If your first answer is incorrect, you should consider
making use of the hints.
Homework Assignment #9 (due Wed 11/16)
#1. A "gauge 8" jumper cable has a diameter d of 0.326 centimeters. The cable carries a current of
30.0 amperes and the electric field in it is 0.062 V/m. (a) What is the resistivity of the jumper
cable? What material is it made of? (b) What electric field would be required to create a current of
30.0 amperes in an aluminum wire of the same diameter? Look up the the resistivity of aluminum
in the book. (c) What electric field would be required to create a current of 30.0 amperes in a
copper "gauge 10" wire with diameter equal to 0.259 centimeters?
#2. A slab of metal of volume V is made into a rod of length L. The rod carries a current I when the
electric field inside it is E. (a) Find the resistivity of the metal in terms of the given symbols. (b)
The rod is now stretched so that its length is doubled. If the electric field remains the same, what is
the new current in the rod? Express your answer in terms of the given symbols. (c) A piece of
copper is made into a rod with a square cross-section. The side of the square is 2.00 centimeters.
An unknown electric field E , directed along the rod, creates a current of 12.0 amperes through the
rod. Find the magnitude of E.
Problem 25-56.
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Homework Assignment #10 (due Mon 11/21 by 5pm)
Go to www.masteringphysics.com and select assignment #10
Homework Assignment #11 (due Mon 11/28)
#1. When we speak of a 100W bulb, we mean one that generates 100W of power when connected
to a source that puts out 120V of potential difference (let us take this to be a DC or direct current
source for simplicity, although it’s actually AC in practice).
(a) Suppose a 150W bulb and a 75W bulb are connected in parallel across a 120V DC source. Draw
a figure of this circuit. Calculate the current through each bulb and the power put out by each.
Which bulb shines more brightly, and by what factor?
(b) Suppose the same two light bulbs are now connected in series to the same source. Again draw a
figure of the circuit and calculate the current through each bulb and the power put out by each.
Which bulb shines more brightly now, and by what factor?
Problem 26.22
Problem 26.66
Homework Assignment #12 (due Wed 11/30 by 5pm)
Go to www.masteringphysics.com and select assignment #12
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