3 Flashcards
Describe what an electric field is.
A place where a charge experiences a force.
Describe what an electric field usually does to charged particles.
An electric field is usually used to accelerate charged particles.
State the meaning of the term ‘electric field strength’.
The force per unit positive charge.
Describe the direction the arrows point in electric field diagrams.
The direction a positive charge would follow.
Describe the electric field strength around a hollow sphere.
Zero inside the sphere and decreasing at 1/r2
.
State the meaning of the term ‘electrostatic potential’.
The work done to bring a positive test charge from infinity to a point in an electric field.
Describe the electrostatic potential around a hollow sphere.
Maximum inside the sphere and decreasing at 1/r.
State the two forces which balance each other in Millikan’s oil drop experiment.
Electrostatic force upwards balanced by weight downwards.
Describe what a magnetic field is.
A place where a moving charge experiences a force.
Describe what a magnetic field usually does to charged particles.
A magnetic field is usually used to deflect charged particles.
Describe what a ferromagnetic material is.
Ferromagnetic materials can be made into magnets. A magnet is held near them and the
dipoles in the materials line up in the same direction.
State the names of three ferromagnetic materials.
Cobalt, Nickel and Iron
Describe the direction of the force between two current carrying wires.
If the current is in the same direction the force is attractive. If the current is in opposite
direction the force is repulsive.
Describe the motion of a charged particle travelling parallel to a magnetic field.
The charged particle will travel at a constant velocity.
Describe the motion of a charged particle travelling perpendicular to a magnetic field.
The charged particle will travel in a circle with the magnetic field providing the central force.
Describe the motion of a charged particle travelling at an angle to a magnetic field.
The charged particle will travel in a helical path as the constant velocity parallel to the
magnetic field combines with the circular motion perpendicular with the magnetic field.
Describe what the time constant is.
The time taken for the current in a capacitive or inductive circuit to reach 63% of its
maximum value during an increase in current or down to 37% of its original value during a
decrease in current.
State what is meant by the term ‘capacitive reactance’.
The opposition to current in a high frequency ac circuit.
State what is meant by the term ‘inductive reactance’.
The opposition to current in a low frequency ac circuit or dc circuit.
Describe how a change in frequency affects the current in a circuit with a capacitor.
An increase in frequency causes an increase in current. A decrease in frequency causes a
decrease in current.
Describe how a change in frequency affects the current in a circuit with an inductor
An increase in frequency causes a decrease in current. A decrease in frequency causes an
increase in current.
Explain why the current in a circuit does not reach its maximum value immediately when a
switch is closed in a circuit with an inductor.
The inductor causes a back emf which opposes the emf of the circuit.
Explain how inductors can be used to generate very large emf’s.
Rapid changes in current can cause large back emf’s to be produced.
Describe a light wave
Light consists of an electric field and a magnetic field oscillating at right angles to each other.
