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VICPhysicsQuick questions
Unit 3: How do fields explain motion and electricity?
Quick questions on Electric fields, Coulomb's law and parallel plates: VCE Physics Unit 3
13short Q&A pairs drawn directly from our worked dot-point answer. For full context and worked exam questions, read the parent dot-point page.
What is the field model?Show answer
An electric field surrounds every electric charge. Another charge placed in the field experiences a force. The field is drawn with field lines that point in the direction of the force on a positive test charge.
What is coulomb's law?Show answer
The electric force between two point charges $q_1$ and $q_2$ separated by distance $r$ is:
What is electric field strength?Show answer
The electric field strength $E$ at a point is the force per unit positive test charge:
What is force and acceleration on a charged particle?Show answer
A charge $q$ in field $E$ feels force $F = qE$. By Newton's second law its acceleration is:
What is comparing electric and gravitational fields?Show answer
The two laws have the same $1/r^2$ form. The key difference is that gravity is always attractive, while the electric force can be either attractive or repulsive.
What is point charge?Show answer
A single point charge $Q$ produces a radial field:
What is parallel plates?Show answer
Two large, parallel, oppositely charged plates separated by distance $d$ with potential difference $V$ produce a uniform field in the gap:
What is direction?Show answer
A positive charge accelerates along the field. A negative charge accelerates opposite to the field.
What is confusing the direction of force on a negative charge?Show answer
The field points from positive to negative; the force on a negative charge is opposite to the field, so it accelerates toward the positive plate.
What is mixing units of $E$?Show answer
N/C and V/m are the same unit. Use whichever matches the rest of the question.
What is forgetting to square the radius?Show answer
$E = kQ/r^2$, not $kQ/r$.
What is applying $E = V/d$ for a point charge?Show answer
$E = V/d$ only works for a uniform field (between parallel plates or inside a long parallel-plate capacitor). Use $E = kQ/r^2$ for a point charge.
What is using nano and milli without converting?Show answer
$1$ nC $= 10^{-9}$ C; $1$ mm $= 10^{-3}$ m. Convert before substituting.