F5-C3 Electricity Flashcards
Define electric field stregth
The electric force acting on a unit positive charge olaced at a point
What is the formula for electric field stregth produced by TWO paprallel plates
E=V/d
V=Voltage
D=distance between 2 plates
Explain twhat happens when a polystyrene ball is placed in betweena positive and a negative plate
- ball does not move because its neutral
- when displaced to negative plate, ball receives negative chatges and bcome negatively charged
- repulsion btween ball n plate causes ball to move towards positive plate
- negatively charged ball releases electrons to positive plate and then ball bcomes poitively charged
- repulsion between like charges and move to negative plate
- ball osscilates
Explain the working principle of lightning conductors on buildings
. When Thunderclouds r nearby, lightning conductor induces positive charges
. + charge will ionise surrounding air by removing - ve charges
. + charged air move upwards and neutralise thunderclouds
The longer a conductor, the ___ its resistance
Higher
What happens to the effective resistance when a resistor is connected in parallel in a circuit?
Effective resistance is zero
Define internal resistance
Resistance caused by electrolyte in dry cell
Define Power
Rate of transfer of electrical energy
Compare the current transferred in a circuit when dry cells are arranged in parallel and the current when dry cells are arranged in series.
Explain
Current transfered when dry cells are parallel > dry cells in series
This is because the internal resistance of dry cells in parallel us smaller than in series
State the formula relating P, power to:
- current and resistance
- current and voltage
- voltage and resistance
P= I^2 R
P=IV
P=V^2 / R
why is a 3 pin plug better than 2 pin plug.
3 pin plug has an earth wire. When there is a leakage in current, current flows into the ground. 3 pin plug is safer.
2 pin plug has no earth wire. When there is leakage, current flows across the metal parts of the plug. Thus, a person who touches it will experience electric shock.
Why must ammeter connected in series to a circuit ?
Ammeter has a low resistance so that its existance will not affect the magnitude of current flow in the circuit.
Why voltmeter connected in parallel?
Voltmeter has high resistance so when connected in parallel, the current flowing through is negligible
Why is the wire in a filament bulb coiled?
Longer wire can ifit into the glass bulb, concentrating the heat to produce brighter light.
