Each day, there are about 45 000 thunderstorms worldwide.  Earth has acquired a net charge from the lightning strikes and therefore surrounds itself with a weak electric field.


Image by 272447 from Pixabay

Investigations of this phenomenon indicate that, near the surface, Earth's electric field is typically 150 N/C directed straight down toward the centre of the planet.  When the field is constant, the field lines are evenly spaced, as indicated in this diagram.

 

Under the right circumstances, a tiny, charged droplet of water could be suspended in Earth's electric field.  In this circumstance, the electrostatic effects counteract the effects of gravity, so the drop would no longer be accelerating toward Earth's surface.

 

You have the tools to analyze this situation, but you have to be careful to use the equations for the electric field correctly.  Remember that one equation deals with the charge on a  test body, while the other equation deals with the charge on the source  of the electric field.

 

 
Self-Check

Answer the following self-check (SC) question then click the "Check your work" bar to assess your response.

 

SC 8.  

Use the diagram of Earth's electric field to determine the sign of the net charge on Earth.

 

   Self-Check Answer

SC 8.  
The diagram of Earth's electric field shows the field lines directed toward the surface of the planet. This indicates that Earth has a net negative charge. The reason is that electric field lines always point toward a negatively charged source. This is because electric field lines always show the way a positive test charge is forced. So if a positive test charge is attracted toward Earth, the planet must have a net negative charge.