Topic 7 Fields Flashcards
Explain how the capacitor discharges. (3)
-Electrons/charge transferred from negatively charged plate to positively charged plate through resistor.
-Hence the charge on capacitor decreases exponentially.
-Until the charge on capacitor is 0.
In an experiment to determine the charge on an electron, negatively charged oil drops are allowed to fall between two parallel metal plates separated by a distance d.
A potential difference (P.D) is applied across the plates.
When the P.D is 0 V the oil drop accelerates to terminal velocity. The P.D is increased. It is observed that at a particular P.D V the oil drop stops falling and remains stationary between the plates.
Explain the motion of the oil drop in terms of the forces acting on it as the P.D is increased from 0 to V. (6)
-At terminal velocity the forces on the drop are balanced/weight=drag.
-The P.D creates an electrostatic force acting upwards on the drop.
-Electrostatic force increases as P.D increases.
-The net upwards force causes drop to have negative acceleration.
-Speed decreases, the drag also decreases.
-Drop remains stationary when weight=electrostatic force.
In an experiment to determine the charge on an electron, negatively charged oil drops are allowed to fall between two parallel metal plates separated by a distance d.
A potential difference (P.D) is applied across the plates.
When the P.D is 0 V the oil drop accelerates to terminal velocity. The P.D is increased. It is observed that at a particular P.D V the oil drop stops falling and remains stationary between the plates.
Explain what would happen to the oil drop if the P.D is increased further. (2)
-Electrostatic force would be greater than downward force.
-So drop accelerates up.
State what is meant by an electric field. (1)
-A region where a charged particle experiences a force.
State the effect of a decreased electric field strength on the equipotential lines. (1)
-Equipotential lines are further apart from one another.
Some flowers are negatively charged and surrounded by an electric field. This helps to attract bees.
A bee has short hairs which are thought to carry charge.
State how the bee might use this to detect the electric field of a flower. (1)
-Charged particle attracts.
The photograph shows a statue of Buddha in Sri Lanka, which is protected by a lightning conductor.
Give a reason why the lightning conductor should be taller than the statue. (1)
-So that the lighting makes contact with conductor instead of statue.
Explain how a step up transformer produces a higher P.D across the secondary coil. (6)
-AC in primary coil produces an alternating magnetic flux in primary coil.
-Iron core is magnetised.
-Iron core links primary and secondary coil.
-As iron core has changing magnetic flux there will be a change in magnetic flux around secondary coil.
-According to faradays law an EMF is induced in secondary coil.
-More turns on secondary coil will increase rate of change of flux linkage according to faradays law.
A simple electric motor consists of a coil that is free to rotate in a magnetic field.
A student connects the motor to an ammeter and a battery.
The switch is closed at time T.
Explain why the current rises to a maximum then decreases.
Your answer should include a reference to Faraday and Lenz’s laws. (6)
-Maximum/initial current = EMF/R.
-Coil rotates.
-Movement of coil changes magnetic flux.
-Which induces an EMF due to faradays law.
-Opposes original EMF/current according to Lenz’s law.
-The faster the coil rotates the larger the EMF.
What is Faradays law?
A changing magnetic flux induces an EMF which induces a current.
What is Lenz’s law?
The direction of induced current is such as to oppose the motion causing it.
