Home Page Textbooks Physics: Principles and Problems Page 651: Section Review

Physics: Principles and Problems

9th Edition

Elliott, Haase, Harper, Herzog, Margaret Zorn, Nelson, Schuler, Zitzewitz

ISBN: 9780078458132

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Page 651: Section Review

Exercise 10

Solution 1

Solution 2

Step 1

1 of 3

We need to discuss whether the magnetic field is real or just a means of scientific modeling.

Step 2

2 of 3

The fact that magnetic field is represented by the magnetic field lines which are modelling tool can sometimes cause confusion,

Step 3

3 of 3

The magnetic field is real, its effects are real and detectable.
It is also measurable quantity.

Step 1

1 of 2

The magnetic field is a real, measurable quantity which is represented by the field lines which are used as modelling tool.

Result

2 of 2

Yes, the magnetic field is real.

Exercise 11

Step 1

1 of 2

In today’s world there is a plenty of magnetic forces around us. We can use a basic compass to detect most of them. Huge electromagnets are used for moving large metal object thus defying gravity, we have levitating globes, one can detect magnetic field bellow the electric lines. And of course the Earth’s magnetic field is everywhere around us.

Result

2 of 2

We can find Earth’s magnetic force wherever we go, we can see magnetic forces of huge electromagnets. For the detection we can simply use a compass.

Exercise 12

Solution 1

Solution 2

Step 1

1 of 3

A current carrying wire is passed through a plate on which there are iron filling sprinked. We need to discuss how will the introduction of another equal wire, close and parallel to the first one affect the magnetic field.
And how it will affect it if the currents flow in opposite direction.

Step 2

2 of 3

If the currents flow in the **same direction**, by following the right-hand rule, the effects of both wires will sum, meaning that there will be **reduced** magnetic field in the area **between** the wires, since fields are in opposite direction at that section and **stronger** on the area on the **outside**, further from the wires.

Step 3

3 of 3

If the currents flow in **opposite** direction, again using the right-hand rule, the field will be **stronger between** the wires since their fields will add up and **weaker on the outside**, further from the wires since magnetic fields act in opposite directions in those areas.

Step 1

1 of 2

In order to answer these questions we are going to use the right-hand rule which tells us that when the currents are parallel and flow in the same direction the resulting magnetic fields are in opposite directions between the wires and in the same direction outside of the two-wire system. That means when in the same direction the magnetic field of the first wire will be reduced in the area towards the second wire and larger on the area opposite of the second wire.

When the currents are flowing in opposite directions the field is larger towards the second wire and smaller outside the of the two-wire system.

Result

2 of 2

1) Same direction currents: the field is smaller between the wires and larger outside of the wires.

2) Opposite direction currents: the field is smaller outside of the system and larger between the wires.

Exercise 13

Solution 1

Solution 2

Step 1

1 of 3

We need to describe right-hand rule used to determine the direction of magnetic field caused by a current flowing through a straight wire.

Step 2

2 of 3

The right-hand rule is a rule that was invented in order to more easily follow the convention regarding the magnetic fields.
Magnetic fields are vector fields, and in a scenario where a conductor is a straight wire, a circular field is created. In order to find its direction, we will use right-hand rule.

Step 3

3 of 3

If we grab a wire with our right hand, with **thumb** pointing in the **direction of the current**, and wrap the remaining **fingers** around the wire, they will show the direction of the **magnetic field**.

Step 1

1 of 2

The right hand rule can be summarized as follows. If we grab the current carrying conductor with our right hand with our thumb pointing in the direction of the current the field lines follow the direction of our fingers.

Result

2 of 2

If we grab the conductor with our right hand with our thumb in the direction of the current then our fingers mimic the field lines.

Exercise 14

Solution 1

Solution 2

Step 1

1 of 2

We need to determine if there will be observable differences if we switch polarity of a magnet placed under a glass sheet covered with iron fillings.

Step 2

2 of 2

When the magnet is turned on, the iron fillings will form a shape of the field lines following them from one pole to another.
Iron fillings will fit on the field lines regardless of the pole orientation, meaning that there will be **no visible change** in case we switch poles of the electromagnet.

Step 1

1 of 2

There would be no visible changes because the field lines shape doesn’t depend on the magnetic polarity.

Result

2 of 2

There would be no visible changes whatsoever.

Exercise 15

Solution 1

Solution 2

Step 1

1 of 3

We have two parallel, horizontal metal rods, one above the other. Upper rod can move vertically.
We need to discuss why is it possible for the top rod to fall down when its direction is reversed.
We also need to discuss what would be the explanation for a scenario in which a top rod is replaced with another rod that falls on the lower one no matter its orientation.

Step 2

2 of 3

The only explanation for the first one is that both rods are actually bar magnets. When the upper one floats on the lower one, their poles are **orientated the same way**; N above N and S above S. This way rods are **repelling** from each other.
When we rotate it front to back, N comes above S and vice versa which causes them to **attract** and a rod to fall down.

Step 3

3 of 3

If the other rod falls down on the lower one no matter its orientation, it simply means it is **not magnetized**. It can be made out of **any kind of material**, because it will fall down due to **gravity** no matter the magnetic attraction or the lack of thereof.

Step 1

1 of 3

a.) The rods are two bar magnets.

When the top rod floats above the bottom one, the north end is above the other north end, and south above south, causing repulsion. When the rods stick together, the north end is above the south end, and south above north, causing attraction.

Step 2

2 of 3

b.) The rod is made of iron, cobalt, or nickel- metals with magnetic properties.

Result

3 of 3

a.) The rods are bar magnets
b.) Iron, nickel, or cobalt

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