Electromagnetism Flashcards
Select all of the following statements that are correct about magnets and magnetic fields
A Magnets can have either a single north pole or a single south pole
B Magnets always have both a north and a south pole
C Magnetic field lines run from a magnet’s south pole to the north pole
D Magnetic field lines run from a magnet’s north pole to the south pole
E The closer the magnetic field lines, the stronger the magnetic field
F Magnetic fields are given the symbol B
B, D, E, and F
What is a magnetic field?
B An area where magnetic objects experience a force
Identify the option that describes how a magnetic field can be created.
A Any metal wire always creates a magnetic field.
B Any material always creates a magnetic field.
C A current carrying wire always creates a magnetic field.
D A stationary electron always creates a magnetic field.
C A current carrying wire always creates a magnetic field.
A bar magnet with no current flowing through it also creates a magnetic field.
Identify the explanation for how the magnetic field is created in a bar magnet with no current flowing through it.
A In a bar magnet, whilst there is no current, the magnetic field is created by the electrons moving around the atomic nuclei.
B In a bar magnet, whilst there is no current, the magnetic field is created by the protons moving around the atomic nuclei.
C In a bar magnet, whilst there is no current, the magnetic field is created by the electrons flowing from one end of the bar to the other
D In a bar magnet, whilst there is no current, the magnetic field is created by the protons flowing through the bar.
A In a bar magnet, whilst there is no current, the magnetic field is created by the electrons moving around the atomic nuclei.
The left hand rule can be useful when solving problems involving magnetic fields.
Identify the option that shows what each finger of the left hand rule represents.
A thumb: force, first finger: field, second finger: current
B thumb: force, first finger: current, second finger: field
C thumb: current, first finger: force, second finger: field
D thumb: current, first finger: field, second finger: force
A thumb: force, first finger: field, second finger: current
A moving electron with a downwards velocity is placed in a uniform magnetic field. The magnetic field is pointing into the paper. Note that an electron has a negative charge
A vertical up
B vertical down
C horizontal to the right
D horizontal to the left
You got it! Perfect!
$\bullet$ The left hand rule is: force - field - current
$\bullet$ We are looking for the direction of the force (thumb)
$\bullet$ We are given the direction of the magnetic field, first finger
$\bullet$ The second finger is the direction of the current, but remember this is the conventional current (i.e. the direction positive charge will move)
$\bullet$ In this example we have an electron. So if the electron is moving downwards, conventional current will be directed upwards
$\bullet$ Point your first finger in the direction of the field (into the page)
$\bullet$ Point the second finger in the direction of the conventional current (upwards)
$\bullet$ Then your thumb should point to the left
$\bullet$ So the direction of the field is horizontal to the left
$\bullet$ Note that the force on the electron is in the opposite direction to the force on the proton in the previous question
State what is meant by ‘step-up’ and ‘step-down’ in this context and explain why these transformers are needed in these positions.
[3 marks]
Step-up involves increasing the voltage / output V higher than input V. AND Step-down decreases the voltage / input V higher than output V.
[Allow step up transformers have more turns on secondary than primary and step down have less turns on secondary than primary. Allow pd, V or volts for voltage.]
Step-up (between power station and transmission line) to reduce current/heat loss (in power lines)
Step-down (between transmission line and home) to reduce voltage to safe levels (in homes)
State and explain one way of improving the efficiency of a transformer.
Laminate the core
[Accept alternative answers accompanied with relevant explanation, e.g. soft magnetic core - reduces energy loss in magnetising/demagnetising; , wrapping coils around same part of core - maximises flux through secondary coil; low resistance wire - reduces energy lost as heat]
[1]
Lamination decreases eddy currents
[1]
