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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?

\begin{align*}
\begin{array}{l}
\rule{0pt}{2.5ex} \ \rule[-1ex]{0pt}{0pt}& \\
\rule{0pt}{2.5ex}\textbf{A.}\rule[-1ex]{0pt}{0pt}\\
\rule{0pt}{2.5ex}\textbf{B.}\rule[-1ex]{0pt}{0pt}\\
\rule{0pt}{2.5ex}\textbf{C.}\rule[-1ex]{0pt}{0pt}\\
\rule{0pt}{2.5ex}\textbf{D.}\rule[-1ex]{0pt}{0pt}\\
\end{array}
\begin{array}{|l|l|}
\hline
\rule{0pt}{2.5ex}\quad \textbf{Magnetic forces}\rule[-1ex]{0pt}{0pt}& \ \textbf{Gravitational forces} \\
\hline
\rule{0pt}{2.5ex}\text{either attract or repel}\rule[-1ex]{0pt}{0pt}&\text{only attract}\\
\hline
\rule{0pt}{2.5ex}\text{only repel}\rule[-1ex]{0pt}{0pt}& \text{neither attract nor repel}\\
\hline
\rule{0pt}{2.5ex}\text{only attract}\rule[-1ex]{0pt}{0pt}& \text{only attract} \\
\hline
\rule{0pt}{2.5ex}\text{either attract or repel}\rule[-1ex]{0pt}{0pt}& \text{either attract or repel} \\
\hline
\end{array}
\end{align*}

Show Answers Only

\(A\)

Show Worked Solution
  • In magnets, like poles repel and opposite poles attract.
  • Gravitational forces are only attractive.

\(\Rightarrow A\)

PHYSICS, M6 2023 HSC 18 MC

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 \(u\) ?


Show Answers Only

\(A\)

Show Worked Solution
  • 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)

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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 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.

PHYSICS M6 2022 HSC 18 MC

A charged oil droplet was observed between metal plates, as shown.
 


 

While the switch was open, the oil droplet moved downwards at a constant speed. After the switch was closed, the oil droplet moved upwards at the same constant speed.

Assume that the only three forces that may act on the oil droplet are the force of gravity, the force due to the electric field and the frictional force between the air and the oil droplet. The magnitudes of these forces are `F_G` (due to gravity), `F_E` (due to the electric field) and `F_F` (due to the frictional force).

Which row of the table shows all the forces affecting the motion of the oil droplet in the direction indicated, and the relationship between these forces?

\begin{align*}
\begin{array}{l}
\rule{0pt}{2.5ex} \ \rule[-1ex]{0pt}{0pt}& \\
\rule{0pt}{2.5ex}\textbf{A.}\rule[-1ex]{0pt}{0pt}\\
\rule{0pt}{2.5ex}\textbf{B.}\rule[-1ex]{0pt}{0pt}\\
\rule{0pt}{2.5ex}\textbf{C.}\rule[-1ex]{0pt}{0pt}\\
\rule{0pt}{2.5ex}\textbf{D.}\rule[-1ex]{0pt}{0pt}\\
\end{array}
\begin{array}{|c|c|}
\hline
\rule{0pt}{2.5ex}\text{Downwards motion}\rule[-1ex]{0pt}{0pt}& \text{Upwards motion} \\
\hline
\rule{0pt}{2.5ex}F_{\text{G}}>F_{\text{F}}\rule[-1ex]{0pt}{0pt}&F_{\text{E}}>F_{\text{F}}\\
\hline
\rule{0pt}{2.5ex}F_{\text{G}}>F_{\text{F}}\rule[-1ex]{0pt}{0pt}& F_{\text{E}}>F_{\text{G}}+F_{\text{F}}\\
\hline
\rule{0pt}{2.5ex}F_{\text{G}}=F_{\text{F}}\rule[-1ex]{0pt}{0pt}& F_{\text{G}}=F_{\text{E}} \\
\hline
\rule{0pt}{2.5ex}F_{\text{G}}=F_{\text{F}}\rule[-1ex]{0pt}{0pt}& F_{\text{E}}=F_{\text{G}}+F_{\text{F}} \\
\hline
\end{array}
\end{align*}

Show Answers Only

\(D\)

Show Worked Solution
  • For the droplet to move at a constant speed, the net force acting on it must be zero.
  • For the downwards motion, this means the downwards gravitational force is equal in magnitude to the upwards frictional force (i.e. \(F_{\text{G}}=F_{\text{F}}\)).
  • For the upwards motion, this means the upwards electric force is equal in magnitude to the sum of the downwards frictional and gravitational forces (i.e. \(F_{\text{E}}=F_{\text{G}}+F_{\text{F}}\)).

\(\Rightarrow D\)


♦♦♦ Mean mark 26%.

PHYSICS, M6 2019 HSC 16 MC

The diagram shows the trajectory of a particle with charge `q` and mass `m` when fired horizontally into a vacuum chamber, where it falls under the influence of gravity.
 

The horizontal distance, `d`, travelled by the particle is recorded.

The experiment is repeated with a uniform vertical electric field applied such that the particle travels the same horizontal distance, `d`, but strikes the upper surface of the chamber.
 

What is the magnitude of the electric field?

  1. `mgq`
  2. `2mgq`
  3. `(mg)/q`
  4. `(2mg)/q`
Show Answers Only

`D`

Show Worked Solution
  • As the particle travels the same distance in both scenarios the magnitude of the force it experiences is the same.
  • Initially, the only force acting on the particle is its weight, `F=mg.`
  • When the electric field is on, the particle experiences an upwards force due to the electric field, and a downwards force due to gravity,  `F=qE-mg.`
  • As these forces have the same magnitude:
`qE-mg` `=mg`  
`qE` `=2mg`  
`E` `=(2mg)/(q)`  

 
`=>D`


♦ Mean mark 42%.

PHYSICS, M6 2021 HSC 18 MC

An evacuated chamber contains a pair of parallel plates connected to a power supply and a switch which is initially closed.

A positively charged mass (•) falls within the chamber, under the influence of gravity, from the position shown.
 

When the mass has fallen half the height of the chamber, the switch is opened.

Which of the following correctly shows the trajectory of the mass?
 

 

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`A`

Show Worked Solution
  • The mass experiences a constant force to the right due to the electric field and a constant force downwards due to gravity.
  • This results in a net force pointing diagonally down and to the right. The mass travels in the direction of this net force.
  • When the switch is opened the mass falls only under the influence of gravity, following a parabolic path.

`=>A`


♦ Mean mark 35%.