P7 - Electromagnetic Effects Flashcards
What is produced around a current carrying wire? [1]
A magnetic field
How can you determine the direction of a magnetic field around a wire? [1]
Using the Right Hand Grip Rule - Thumb is the direction of current, the field lines wrap around in the direction of your fingers
What is a solenoid? [1]
A coil of wire with a magnetic field, which can be used as an electromagnet
How can you increase the strength of a solenoid magnet? [3]
Using an iron core / Increasing the number of turns in the coil / Increasing the current
What is the motor effect? [1]
When a current carrying wire is placed in a magnetic field it experiences a force, pusing the wire out/away from the field
How can you predict the direction of the motor effect? [3]
Flemings Left Hand Rule / Thumb = Movement, First finger = Field, Second finger = Current
What kind of current is used in Fleming’s Left Hand Rule? [1]
Conventional current (positive to negative)
What factors affect the strength of the electromotive force (e.m.f)? [3]
The length of wire placed in the field / the current in the wire / the strength of the permanent field
What are 4 main parts of a motor? [4]
Magnets / coil of wire / power supply / split ring commutator
What is the role of the split ring commutator in a motor? [1]
Reverses the current every half turn
What is electromagnetic induction? [1]
The production of a potential difference caused by relative movement between a conductor and a magnetic field
Describe how an electrical generator works [4]
A turbine spins the coil of wire between the magnets / the wire cuts through the magnetic field experiencing a changing magnetic field / a potential difference is induced / a current is produced
What is the difference between direct current (D.C) and alternating current (A.C)? [2]
Direct current only flows in one direction / Alternating current flows in both directions
Compare a motor, AC generator and DC generator in terms of a power supply and slit ring commutator [2]
Motor has a power supply but generators do not / motor and DC generator has a split ring commutator but an AC generator has slip rings
What is the role of the split ring commutator in a DC generator? [1]
Ensures the current only flows in one direction
What is the role of the slip rings in an AC generator? [1]
Ensures current can flow in both directions
Describe how transformers work [2]
An alternating current flows through the primary coil, producing an alternating magnetic field / this causes the secondary coil to experience a changing magnetic field, inducing a potential difference which produces an alternating current in the secondary coil
Why do step up transformers increase voltage? [1]
There are more coils in the secondary coil so a larger potential difference is induced
What is the core made of in a transformer? [1]
Soft iron core
Recall the equation that relates the voltage and number of coils in the primary and secondary coils in a transformer [1]
(Vₚ/Vₛ) = (Nₚ/Nₛ)
State one assumption used in transformer calculations [1]
The transformer is 100% efficient (the power is assumed to be the same in both coils)
Explain why a step up transformer is useful in the transmission of high voltage electricity [3]
P=IV - Power lines have to transmit huge amounts of power - to achieve this you would want a high voltage and high current / High current produces a lot of wasted heat energy due to resistance / We compensate for this by using an extremely high voltage (400,000V)
Recall the equation that relates current and voltage in the primary and secondary coils in a transformer [1]
(Iₚ/Vₚ) = (Iₛ/Vₛ)
