Electric Fields

The electric field strength between a pair of parallel plates is E. The separation of the plates is doubled and the potential difference between the plates is increased by a factor of four.

What is the new electric field strength?

• E

• 2E

• 4E

• 8E

Which the following statements about an electric field is incorrect?

• The electric field strength due to a point charge varies as 1/r² where r is the distance from the charge.

• Electric field strenggth is a vector quantity.

• The electric field strength at a point is a measure of the force exerted on a unit positive charge at the point.

• The electric field strength is zero at all points where the potential is zero.

Which diagram represents the electric fields of a negative point charge, shown by º

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Which diagram represents the electric field in the vicinity of a positive electric charge of magnitude Q?

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The large horizontal metal plates are separated by 4 mm. The lower plate is at a potential of -6 V.

What potential should be applied to the upper plate to create an electric field of strength 4000 Vm^-1 upwards in the space between the plates?

• +22 V

• -10 V

• +10 V

• -22 V

An electron of charge e is introduced between two metal plates a distance d apart.

A potential difference V is applied to the plates as shown in the diagram.

Which expression gives the electric force F on the electron?

• $\frac{eV}{d}$

• $eVd$

• $\frac{V}{ed}$

• $\frac{dV}{e}$

Two large parallel plates are separated by 5.0 mm. The upper plate is at a potential of -8.0 V.

What potential should be applied to the lower plate to create an electric field strength of 2500 Vm^-1 upwards in the space between the plates?

• 4.5 V

• -12.5 V

• 12.5 V

• -20.5 V

Electric field is dimensionally equivalent to which of the following?

• Nm/C

• N/C

• Nm²/C

• N/C²

The beam of electrons that hits the screen of an oscilloscope is moved up and down by:

• gravity

• varying the electron's charge

• electrical charges on deflecting plates

• electrical repulsion between electrons

The number of electric field lines passing through a unit cross sectional area is indicative of:

• field direction

• field strength

• charge motion

• charge density