Section 3 Flashcards
Explain how a falling object reaches terminal velocity
There is a net force downwards
So it accelerates downwards because of F=ma
There is a force of drag upwards
Drag increases as speed increases
Until the drag force is equal to the speed
Then, the net force is zero
So it moves at constant speed, due to Newton’s First Law
Describe how an earth wire acts as a safety feature
The earth wire is connected to the metal casing of an object
So if the casing becomes live..
The earth wire provides a low resistance path to earth
Therefore, if there is a large current in the earth wire
The fuse melts and breaks
This breaks the circuit and the current stops
Why should an appliance with a metal case have an earth wire
It has a metal case
Metals conduct electricity
So, the earth wire is needed to stop the user getting shock
Why does the resistance of a lamp change as you increase the voltage
As the voltage increases, more current flows and the temperature of the filament increases
This means there are more collisions between electrons and the atoms in the filament
Which causes a greater resistance
