9702 · 18.1
Electric fields and field lines flashcards
Revision flashcards for Cambridge 9702 Electric fields and field lines (syllabus 18.1). Flip, recall, then mark a real past-paper question.
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How is electric field strength (E) defined?
It is the electrostatic force experienced per unit positive test charge ($E=F/Q$). It's a vector quantity.
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What does the density of electric field lines indicate?
The strength of the electric field; denser (closer) lines signify a stronger field.
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How do electric field lines originate and terminate?
They originate from positive charges and terminate on negative charges, or extend to infinity.
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State Coulomb's Law for the force between two point charges.
$F = \frac{1}{4\pi\epsilon_0} \frac{Q_1Q_2}{r^2}$, where $Q_1, Q_2$ are charges, $r$ is separation, and $\epsilon_0$ is permittivity of free space.
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How are electric field lines represented in a uniform electric field?
As parallel and equally spaced straight lines.
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What is the direction of the electric field at any point?
It is the direction of the force that a positive test charge would experience if placed at that point.
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What does $\epsilon_0$ represent in Coulomb's Law?
The permittivity of free space, a fundamental constant that describes how an electric field permeates a vacuum.
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What path does a charged particle follow if fired perpendicular to a uniform electric field?
A parabolic path, similar to projectile motion under gravity.
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How do positive and negative charges accelerate in an electric field?
Positive charges accelerate in the direction of the field; negative charges accelerate opposite to it.
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What is the relationship between electric field lines and equipotential lines?
Electric field lines are always perpendicular to equipotential lines.
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What is the principle of superposition for electric fields?
The net electric field at a point due to multiple charges is the vector sum of the individual electric fields produced by each charge at that point. $E_{net} = \sum E_i$.
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What is the electric field inside a hollow, charged conducting sphere in electrostatic equilibrium?
Zero. All the net charge resides on the outer surface, and the fields from these charges cancel out completely inside the conductor.
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An electron and a proton are in the same uniform electric field. Compare the forces they experience and their accelerations.
They experience forces of equal magnitude ($F=Eq$) but in opposite directions. Since the proton is much more massive ($m_p > m_e$), its acceleration ($a=F/m$) will be much smaller than the electron's.
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What are the two common, equivalent units for electric field strength?
Newtons per Coulomb (N C⁻¹) derived from $E=F/Q$, and Volts per metre (V m⁻¹) derived from $E=V/d$. They are dimensionally equivalent.