# 21.2.3 E Fields v G Fields

### E Fields v G Fields

• Electric field strength (E) and gravitational field strength (g) have very similar equations
• Despite a few differences, they are analogous to one another in many ways
• Origin of the force:
• G fields: Mass M
• E fields: Charge Q
• Field strength:
• G fields:

• E fields:

• Field strength due to a point mass/charge
• G fields:

• E fields:

• Potential:
• G fields: Work done in bringing a unit mass from infinity to that point
• E fields: Work done in bringing a unit charge from infinity to that point
• Potential of a point mass/charge:
• G fields:

• E fields:

The sign depends on the charge

• Potential energy:
• G fields: G.P.E = Mɸ
• E fields: E.P.E = QV
• Force in a radial field:
• G fields: Always attractive
• E fields: Attractive for a negative charge, repulsive around a positive charge

#### Exam Tip

This topic could come up as long structured answer question, practice summing up this information as you would for a 6 mark question.

### Author: Katie

Katie has always been passionate about the sciences, and completed a degree in Astrophysics at Sheffield University. She decided that she wanted to inspire other young people, so moved to Bristol to complete a PGCE in Secondary Science. She particularly loves creating fun and absorbing materials to help students achieve their exam potential.
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