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American System Physics

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Representing Motion

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Gravitation

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Quiz

20.2 Magnetic Effect of a Current and Electromagnets – Quiz

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Magnetic Effect of a Current and Electromagnets American Physics quiz: free practice for American System Physics. Work through this Magnetic Effect of a Current and Electromagnets American Physics quiz and get instant feedback on every answer. If you get stuck, review the 20.2 Magnetic Effect of a Current and Electromagnets — Notes lesson. More practice: American System Physics — all units. Syllabus: OpenStax free science textbooks.

  • Questions count: 50
  • Passing grade: A-
  • Time limit:
Start Quiz
1.
The diagram is a top view of a straight wire carrying a current out of the page, with field lines drawn around it (no arrows shown). Which way does a compass at point P point?
Dr Dabour Hub Academy - figure 1
Towards the top of the page (up)
Towards the bottom of the page (down)
Away from the wire (right)
Towards the wire (left)
2.
The field lines around a current-carrying wire are drawn in the diagram. At which labelled point is the magnetic field strongest?
Dr Dabour Hub Academy - figure 2
B
C
A
D
3.
The diagram shows a solenoid. The red arrow shows the direction of conventional current in the front of each turn. What pole is at end Y?
Dr Dabour Hub Academy - figure 3
South pole
No pole; solenoids have no poles
Both poles, because the field is uniform
North pole
4.
The graph shows the number of paper clips an electromagnet lifted for two coils. Which conclusion is best supported?
Dr Dabour Hub Academy - figure 4
Strength depends only on the number of turns
More turns and more current both increase strength, but the gain per amp falls at high current
Strength is directly proportional to current at all currents
The 20-turn coil is stronger at high current
5.
The graph shows the field measured at different distances from a straight wire carrying a steady current. What is the field at 6 cm compared with 2 cm?
Dr Dabour Hub Academy - figure 5
Three times as strong
Half as strong
One third as strong
The same strength
6.
The diagram shows a relay. Which pairing of label and part is correct?
Dr Dabour Hub Academy - figure 6
A — contacts in the output circuit
B — spring that opens the contacts
D — coil of the electromagnet
C — soft-iron armature that pivots when attracted
7.
The circuit shown is used to investigate how current affects the strength of an electromagnet. What is the role of the variable resistor?
Dr Dabour Hub Academy - figure 7
To set different currents, read on the ammeter, while the number of turns stays fixed
To measure the strength of the electromagnet
To change the number of turns on the nail
To keep the electromagnet switched on permanently
8.
An electromagnet with a fixed number of turns lifts the numbers of paper clips shown. Assuming clips lifted is proportional to current, how many clips would it lift at 0.90 A?
15
27
30
9
9.
The table shows results for coils with different numbers of turns at a fixed current of 0.50 A. Which conclusion is supported?
Fewer turns give a stronger electromagnet
The number of turns has no effect
More turns give a stronger electromagnet
Strength doubles for every extra turn
10.
A student repeats the paper clip test three times at each current. Using the table, which reading is anomalous?
0.20 A, trial 1
0.40 A, trial 3
0.60 A, trial 3
0.60 A, trial 2
11.
Using the table of changes made to an electromagnet, which change would reverse its poles without changing its strength?
Change 3
Change 1
Change 2
Change 4
12.
A compass is placed at different distances from a wire carrying a steady current (Oersted’s experiment). Using the table, what can be concluded?
The field is the same at all distances
The compass is deflected only by the Earth
The magnetic field of the current weakens with distance from the wire
The field grows stronger further from the wire
13.
A magnetic circuit breaker is designed to trip at 15 A. Using the table, in which situation does it open?
Situation A
Situation B
Situation C
Situation D
14.
Using the table of devices, which pairing of device and how its electromagnet is used is correct?
Electric bell — attracts an armature that breaks its own circuit repeatedly
Relay — the coil current flows directly through the output device
Scrapyard crane — uses a steel core so the car stays attached
Circuit breaker — the magnet closes a switch when current is too large
15.
What did Oersted observe that showed a current produces a magnetic field?
A wire got hot when current flowed
A compass needle was deflected by a nearby wire carrying a current
A magnet produced a current in a coil
Iron filings were attracted to a battery
16.
In the right-hand grip rule for a straight wire, what do the thumb and fingers represent?
Thumb: field; fingers: current
Thumb: electron flow; fingers: force
Thumb: conventional current; curled fingers: field direction
Thumb: force; fingers: field
17.
Why is soft iron, not steel, used as the core of an electromagnet?
Steel is not a magnetic material
Soft iron conducts the current better
Steel makes the field weaker
Soft iron loses its magnetism when the current is switched off
18.
Why does adding a soft-iron core make an electromagnet much stronger?
The core becomes magnetised by induction and adds its field to the coil’s field
The core carries extra current
The core increases the number of turns
The core increases the voltage of the supply
19.
Why is a relay used to switch a car’s starter motor?
It makes the starter current smaller
A small, safe current in the ignition circuit can switch a separate circuit carrying a very large current
It changes d.c. into a.c.
It stores energy for the motor
20.
In an electric bell, what happens immediately after the hammer strikes the gong?
The current increases and the hammer stays against the gong
The core becomes a permanent magnet
The contact breaks, the electromagnet switches off and the spring pulls the armature back
The battery reverses its current
21.
A student’s electromagnet gets hot during the experiment and results drift. Which improvement is best?
Use a steel core
Increase the current further
Remove the ammeter
Switch off between readings to prevent overheating
22.
Which plan correctly tests the effect of the number of turns on electromagnet strength?
Change the turns, keep the current, core and clips the same, and count clips lifted
Change the turns and the current together
Keep the turns fixed and change the core material
Change the turns and use a different size of paper clip each time
23.
How does the field inside a long solenoid compare with the field outside it?
Inside it is zero; outside it is uniform
Inside it is strong and uniform; outside it is like a bar magnet’s field
Inside it forms concentric circles
Inside and outside are both uniform and equal
24.
Why is the number of paper clips lifted only an approximate measure of electromagnet strength?
Paper clips are non-magnetic
The ammeter cannot read currents
Clips can only be counted in whole numbers and the result depends on how they hang
The clips change the current
25.
Electromagnet designs can be changed in different ways. Which change is matched with its correct effect on field strength?
Reduce the number of turns — stronger
Add a soft-iron core — much stronger
Switch off the current — same strength
Reverse the current — weaker
26.
Different current-carrying conductors produce different field shapes. Which conductor is matched with its correct pattern?
Straight wire — uniform parallel lines
Flat circular coil — concentric circles only around the centre
Solenoid — uniform parallel lines inside, bar-magnet shape outside
Solenoid — lines that cross in the middle
27.
Each electromagnetic device relies on a particular part. Which device is matched with its key moving part?
Electric bell — rotating commutator
Circuit breaker — permanent steel core
Solenoid — spinning brushes
Relay — pivoting armature that closes contacts
28.
A scrapyard crane uses an electromagnet to move old cars. Why is an electromagnet better than a permanent magnet for this job?
It can be switched off to drop the car where needed
It never needs electricity
It attracts copper and aluminium as well
It keeps its magnetism when switched off
29.
The current in a straight wire is increased. How does the field pattern drawn around it change?
The circles become straight lines
The circles are drawn closer together, showing a stronger field
The circles reverse direction
The circles move farther apart
30.
A long coil of wire that produces a field like a bar magnet when it carries a current is called a _____.
solenoid
relay
armature
commutator
31.
The piece of soft iron moved by the electromagnet in a relay or electric bell is called the _____.
core
armature
coil
brush
32.
An electromagnet lifts 8 clips at 0.25 A. If clips are proportional to current, at 0.75 A it should lift _____ clips.
16
11
24
3
33.
The SI unit of magnetic flux density is the _____.
weber
ampere
henry
tesla
34.
Seen from one end, the current in a solenoid flows clockwise, so that end is a _____ pole.
south
north
neutral
positive
35.
The diagram shows a wire carrying current into the page. At point Q, directly below the wire, the magnetic field points to the left. True or false?
Dr Dabour Hub Academy - figure 8
False, it points to the right
True
False, it points towards the wire
False, there is no field below a wire
36.
In this electromagnet the current in the front of each turn flows upwards (red arrow). End X is a north pole. True or false?
Dr Dabour Hub Academy - figure 9
True
False, both ends are north poles
False, the iron core has no poles
False, end X is a south pole
37.
A student looks at the end of a solenoid and records the direction of current in the table. The table correctly identifies both poles. True or false?
True
False
True only with an iron core
False, a solenoid has no poles
38.
The magnetic field lines around a straight current-carrying wire are concentric circles centred on the wire. True or false?
False, they run parallel to the wire
False, they point away from the wire
True only for a.c.
True
39.
Reversing the current in a wire reverses the direction of the magnetic field around it. True or false?
True
False, the field direction is fixed
False, the field disappears
True only near the wire
40.
Reversing the current in an electromagnet makes it weaker. True or false?
True
False
True only with an iron core
False, it makes it stronger
41.
Looking at the end of a solenoid, an anticlockwise current means that end is a north pole. True or false?
False, it is a south pole
False, the end has no pole
True
True only for d.c. coils without a core
42.
The right-hand grip rule uses the direction of electron flow. True or false?
True
True only for solenoids
True only in metals
False
43.
An electromagnet can be switched on and off and its strength adjusted, unlike a permanent magnet. True or false?
True
False, it can never be switched off
False, its strength is fixed
True only with a steel core
44.
Doubling the distance from a straight wire makes the magnetic field stronger. True or false?
True
False
True only for large currents
False, it has no effect
45.
A student turns up the supply so that a larger current passes through a solenoid; the field inside the coil becomes stronger. True or false?
False, it reduces the field
False, only turns matter
True
True only when the current is reversed
46.
A relay allows a low-voltage circuit to safely control a high-voltage circuit. True or false?
False, both circuits carry the same current
False, a relay only works with a.c.
True only for electric bells
True
47.
If a steel core were used in an electric bell, the armature might stay stuck to the magnet. True or false?
True
False, steel loses magnetism faster
False, the bell would ring louder
False, steel is non-magnetic
48.
A magnetic circuit breaker can be reset after it trips. True or false?
False, it must be replaced like a fuse
True
False, it never trips
True only for a.c.
49.
When investigating electromagnet strength, it is a fair test to change the current and the number of turns at the same time. True or false?
True
True if the core is soft iron
False
True only for large currents
50.
Magnetic fields from electric currents are used in loudspeakers, MRI scanners and maglev trains. True or false?
False, only permanent magnets are used
False, only in MRI scanners
True only in loudspeakers
True
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