QCE Physics Questions Thread

[jasmine24]

hi, i was wondering how Lenz's law is consistent with the principle of conversation of energy
Thank you

[Bri MT]

hi, i was wondering how Lenz's law is consistent with the principle of conversation of energy
Thank you

Hi,

Hopefully this reaches you before paper 2!

I encourage you to draw out how you could get a situation with infinite electrical energy if Lenz's law wasn't true by having positive feedback loop of: more current -> more change in flux -> more current -> more change in flux etc.

Another way to think about it is to take the situation of moving a coil towards a bar magnet. As the coil moves the change in flux will induce current in the coil and thus the coil will generate a magnetic field. This magnetic field will have a north and south end and consequently there will be attraction or repulsion between the coil and bar magnet. This attractive or repulsive force will act over the displacement of the coil (W=Fx) and this work balances the change in electrical energy.

I've included a rough diagram below where you can see that as the distance between the bar magnet and loop decreases the generated magnetic field is such as to generate repelling force.

[jasmine24]

For my SI, i'm doing inclined planes and one of the suggested improvements was using a longer incline (I'm measuring time taken for object to travel down the inclined plane) because it would give more consistent results but I'm not sure how it would and was wondering if anybody knew why 

[fun_jirachi]

The longer the plane is, the longer it takes for the object to roll down the plane. This increases the consistency of results because random error will comparatively be a smaller percentage of the time taken than if you had a smaller incline.

Consider fixing random error at ±0.1s. A longer plane may take 3s + random error, while a smaller plane may take 2s + random error. This is an unrealistic example but hopefully, this demonstrates that longer inclines will minimise the impact of random error on your experiment (thus providing more consistent results). It's the same reason why we choose compounds of high molar mass for standard solutions in chemistry.

Hope this helps

[jasmine24]

what is the relationship between the length of an inclined plane and acceleration? All ik is that as displacement increases, acceleration decreases but I'm not sure why
TIA

[K.Smithy]

what is the relationship between the length of an inclined plane and acceleration? All ik is that as displacement increases, acceleration decreases but I'm not sure why
TIA

As you increase the length of a ramp, you decrease the angle that the ramp has to make with the ground.
A greater angle will result in greater acceleration. Thus, a shorter ramp/shorter displacement will result in increased acceleration. Whereas, a longer ramp will result in decreased acceleration.

I have drawn a little picture to help us think about this (prepare yourself for what is sure to be the best drawing you've ever seen in your entire life - no cap):

As you can see on the image above, we have two people who are about to roll down a hill. In condition 1, the ramp is longer - meaning the angle is smaller. In condition 2, the ramp is shorter - meaning the angle is larger.
Who do you think will roll down the hill faster? The person in condition two, right? Yes. Honestly, that hill looks like it would hurt to roll down lol.

Hope this makes sense

[justsomerandom21]

Hi does anyone recommend memorising all the notes we're given in class by our teachers or just the syllabus dot points?

[K.Smithy]

Hi does anyone recommend memorising all the notes we're given in class by our teachers or just the syllabus dot points?

I had my fair share of teachers who covered content that wasn't super important. I would recommend putting all of the syllabus dot points onto a word document and filling your notes underneath each dot point so that you know you've covered it all. At least for the theory-based dot points. For the practical-based calculation type dot points, just do practice questions. I noticed you asked the same question for biology, I recommend this method for that as well. It ensures that you have everything you need.

[justsomerandom21]

I had my fair share of teachers who covered content that wasn't super important. I would recommend putting all of the syllabus dot points onto a word document and filling your notes underneath each dot point so that you know you've covered it all. At least for the theory-based dot points. For the practical-based calculation type dot points, just do practice questions. I noticed you asked the same question for biology, I recommend this method for that as well. It ensures that you have everything you need.

Thanks so much for the advice!! I've had a bit of a hectic year with so many of my teachers leaving my school and me just trying to survive the school year...I really appreciate this!

[jasmine24]

just a quick question, if a study I'm using may be slightly outdated, does it affect its reliability or validity?
thanks!

[Billuminati]

just a quick question, if a study I'm using may be slightly outdated, does it affect its reliability or validity?
thanks!

If the source you’re trying to reference is designed well and controls all variables except for the independent variable, then it’s valid. If its result data points are pretty consistent with each other, then it’s also reliable. However given its age, there may be new advances in the field such that the values reported may not necessarily be accurate anymore ie close to the true values that we know of now

[jinx_58]

Hey everyone.

What would be a good example of Newton's first, second and third laws?

Thanks,
- jinx_58

[K.Smithy]

Hey everyone.

What would be a good example of Newton's first, second and third laws?

Thanks,
- jinx_58

Hey Jinx_58,

1st Law Example: the experience of being "thrown" forward when your car comes to an abrupt stop. Why is this an example of Newton's first law? Well, the first law is known as the law of inertia (where inertia is the tendency of a body to resist a change in velocity). You'll often hear: "A body in motion remains in motion, and a body that is stationary remains stationary, unless acted upon by an unbalanced external force." So, with the example of being thrown forward when your car comes to a stop... Your body's inertia wants to keep you moving forward, however the car (acting as an unbalanced external force) stops you from being able to continue on this path.

2nd Law Example: If you have 2 boxes (one of mass 10kg and one of mass 100kg) and you want to push them both forward with an acceleration of 0.5ms^-2, you will require much more force to push the 100kg box at that speed, than you would the 10kg box.

3rd Law Example: If you throw a tennis ball at the ground it will bounce back up into the air. Why? Because newton's third law of motion states that every action has an equal and opposite reaction. When you throw the ball at the ground, it exerts a force on the ground. The ground also exerts the same magnitude of force back on the ball - only it acts upwards. Thus, the ball is propelled upwards.

Hope this helps

[jinx_58]

Thank you!

[jinx_58]

Greetings.

I'm having trouble meeting the following Unit 1 success criteria:
1. explain that a system with thermal energy has the capacity to do mechanical work
2. explain natural radioactive decay in terms of stability
3. describe energy in terms of electron volts (eV) and joules (J)


I'm having trouble meeting the following Unit 2 success criteria:
1. explain the formation of standing waves in terms of superposition with reference to constructive and destructive interference, and nodes and antinodes.
2. construct free-body diagrams representing forces acting on an object
3. describe polarisation using a transverse wave model
4. contrast the speed of light and the speed of mechanical waves

Any help would be appreciated.

Regards,
 jinx_58