smc-3693-70-Electric vs gravitational

PHYSICS, M6 2019 VCE 1 MC

Magnetic and gravitational forces have a variety of properties.

Which of the following best describes the attraction/repulsion properties of magnetic and gravitational forces?

	Magnetic forces	Gravitational forces
A.	either attract or repel	only attract
B.	only repel	neither attract nor repel
C.	only attract	only attract
D.	either attract or repel	either attract or repel

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\(A\)

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→ In magnets, like poles repel and opposite poles attract.

→ Gravitational forces are only attractive.

\(\Rightarrow A\)

The diagrams show the trajectories of two particles with the same mass and charge and which initially have the same velocity \(u\), as shown. The subsequent motion of each particle is determined by its properties and by its interaction with the field in which it is moving.

\(X\) and \(Y\) represent the landing points in Figures \(\text{I}\) and \(\text{II}\).

Which row of the table shows the correct paths of the particles if the mass of each is increased by the same amount and they are given the same initial velocity \(u\) ?

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\(A\)

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→ The motion of a projectile within a gravitational field is independent of the mass of the projectile as all projectiles accelerate the same under gravity.

→ Increasing the mass of the particle within the gravitational field will have no effect on the range of the projectile, hence it will still land at \(X\).

→ However, in an electric field the force on a charged particle is given by \(F=qE\) and using Newton’s second law of motion, the equation can be rewritten as

\(ma=qE\ \ \Rightarrow \ \ a=\dfrac{qE}{m}\ \ \Rightarrow\ \ a \propto \dfrac{1}{m} \)

→ By increasing the mass of the particle, the acceleration of the particle in the electric field decreases.

→ It takes a greater time to reach the ground, therefore the range of the particle is increased.

\(\Rightarrow A\)

♦ Mean mark 45%.

PHYSICS, M6 2018 HSC 26

Outline the similarities and differences between the effects of electric fields and gravitational fields on matter. In your answer, refer to the definitions of these fields. (4 marks)

--- 12 WORK AREA LINES (style=lined) ---

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Differences in effects:

→ Electric fields are regions in space where a force acts on a charged particle whereas gravitational fields are regions in space where a force acts on an object with mass due to the influence of another object with mass.

→ Electric field strength is defined by `E=(F)/(q)`, or force per unit charge.

→ Gravitational field strength is defined with `g=(F)/(m)`, or force per unit mass.

→ Electric fields can produce forces of repulsion (due to like charges) while gravitational fields can only produce forces of attraction.

Similarities:

→ Both fields are able to produce forces of attraction.

→ Electric and gravitational fields vary in strength due to magnitudes of charge and mass respectively.

→ The strength of both fields is inversely proportional to the distance of separation from a point charge or mass.

→ Gravity is a significantly weaker fundamental force compared to electromagnetism.

Show Worked Solution

Differences in effects:

→ Electric field strength is defined by `E=(F)/(q)`, or force per unit charge.

→ Gravitational field strength is defined with `g=(F)/(m)`, or force per unit mass.

→ Electric fields can produce forces of repulsion (due to like charges) while gravitational fields can only produce forces of attraction.

Similarities:

→ Both fields are able to produce forces of attraction.

→ Electric and gravitational fields vary in strength due to magnitudes of charge and mass respectively.

→ The strength of both fields is inversely proportional to the distance of separation from a point charge or mass.

→ Gravity is a significantly weaker fundamental force compared to electromagnetism.