Chp 15: EM Flashcards
define Magnetic Field:
A magnetic field is a region of space where a magnetic material, a current-carrying conductor or a moving charge experiences a magnetic force.
define Magnetic Flux Density:
The magnetic flux density of a magnetic field is numerically equal to the magnetic force per unit length of a long straight conductor carrying a unit current placed at right angles to the magnetic field. The magnetic force acts in a direction perpendicular to both the current and the magnetic field.
define The tesla:
1 tesla is the uniform magnetic flux density which act normal to a long straight wire carrying current of 1 ampere, causes a magnetic force per unit length of 1 newton per metre acting on the wire.
What is the effect of a ferrous core in a solenoid?
A ferrous (iron) core has the ability to align its dipoles in the direction of an external magnetic field. By inserting a ferrous core into a solenoid, the field lines are concentrated, thus strengthening the field. The ferrous core becomes magnetized and results in a much stronger magnetic field in the same direction because the resultant magnetic flux density is the vector sum of both magnetic flux densities produced by the original solenoid and the iron core.
By reference to the flux pattern of the magnetic field in a solenoid, suggest the difference between the magnitude of the magnetic flux density at the ends of the solenoid compared with at that at the centre.
The magnetic field lines would spread further apart at the ends of the solenoids. Hence, the number of field lines per unit cross-sectional area perpendicular to the magnetic field lines is less compared to the centre of the solenoid. The magnitude of the magnetic flux density at the ends lesser than that at the centre.
Explain why no magnetic force acts on a straight current-carrying conductor placed along the axis of the solenoid.
When the straight current-carrying conductor is placed along the axis of the solenoid, it is parallel to the B-field produced by the solenoid. By FLHR, since current // B-field, the wire experiences no magnetic force.
What are the differences in the deflection of a charged particle in a magnetic field vs in an electric field?
1.Magnetic field can exert a magnetic force only on a moving (non-parallel to the field) charged particle. Stationary charge particles do not experience a force.
1.Electric field will always exert an electric force on a charged particle, whether it is stationary or not.
2.Magnetic force is perpendicular to the magnetic field and velocity of the charged particle.
2.Electric force acts along the direction of the electric field depending on the polarity of the charged particle.
3.Magnetic force is dependent on the speed and direction of motion of the charged particle.
3.Electric force is not dependent on the speed and direction of the charged particle.
4.Circular motion is obtained when a charged particle enters the uniform magnetic field perpendicularly.
4.Parabolic motion is obtained when a charged particle enters the uniform electric field perpendicularly.
2 straight long parallel wires carrying current upwards in the same direction experience a force between them. State the direction of the forces.
By right hand grip rule, wire 1 produces a magnetic field at wire 2 into the page that interacts with the current in wire 2. By Fleming’s left-hand rule, wire 2 experiences a leftward magnetic force. Similarly, by right hand grip rule, wire 2 produces a magnetic field at wire 1 out the page that interacts with the current in wire 1. By Fleming’s left-hand rule, wire 1 experiences a rightward magnetic force. The magnetic force between the 2 wires is attractive.
Explain how it is possible to select ions of a particular speed by changing the electric and magnetic fields.
The electric force and the magnetic force on the ions must act in opposite directions. The electric force acting on the ion is given by FE = qE while the magnetic force acting on the ion is given by FB = Bqv, as FE = FB, only ions with speed v = E/B can pass through the cross fields undeflected while ions of other speeds will be deflected.
How charged particles undergo helical path?
As the charge enters the magnetic field, the component of its velocity parallel to the magnetic field causes the charge to move with constant speed in the parallel direction. In addition to this, the velocity that is perpendicular to the magnetic field causes a magnetic force that acts perpendicularly to the magnetic field which provides the centripetal force for the charge to be in a uniform circular motion perpendicular to the magnetic field. The combination of these results in a helical path.
Why path of electrons in a uniform magnetic field is circular?
By Fleming’s left-hand rule, the magnetic force acting on the charge is always perpendicular to it motion. Since the speed of the charge is constant, the magnetic force acting on the charge is constant in magnitude. Therefore, the magnetic force provides for the centripetal force which is constant in magnitude as well, the charge undergoes a uniform circular motion of constant radius.
