Test charge

Definition

A test charge is a hypothetical charge with negligible magnitude used to measure the electric field strength at a point without disturbing the field itself. It is typically positive and small enough not to influence nearby charges or fields.

5 Must Know Facts For Your Next Test

1. Test charge is assumed to be infinitesimally small to avoid altering the electric field it measures.
2. It is usually positive, simplifying calculations and conceptual understanding of the direction of electric fields.
3. The force experienced by a test charge in an electric field is given by $\vec{F} = q\vec{E}$, where $q$ is the test charge and $\vec{E}$ is the electric field.
4. The concept of a test charge helps in visualizing and measuring electric fields around charged objects.
5. Electric potential at a point can also be defined using a test charge: it’s the work done per unit charge to move the test charge from infinity to that point.

Review Questions

• Why must a test charge be infinitesimally small?
• How does the direction of an electric field relate to a positively charged test charge?
• What equation represents the force on a test charge in an electric field?

Related terms

Electric Field: A region around a charged particle where other charges experience an electrostatic force. Represented by $\vec{E}$, it has both magnitude and direction.

Coulomb's Law: $F = k \frac{|q_1 q_2|}{r^2}$, describes the electrostatic force between two charges separated by distance $r$. Here, $k$ is Coulomb's constant.

Electric Potential: $V$, defined as the work done per unit charge in bringing a positive test charge from infinity to that point in space without acceleration.