# Multiple choice??? (1 Viewer)

#### Lingb

##### New Member
Does anyone have the correct answers for the multiple choices that they want to post??? perhaps checked by your teacher or something???

cheers

#### mattmaug

##### New Member
8 is c as there is positive gradient at the beginning whereas d says there is negative

12 isnt b as the interference pattern is formed all around it, rather than just behind it like it says in b. i said it was a

#### slasher3689

##### New Member
Hmm according to flowergirls answers, I got 10/15. Im really annoyed because I got everything right except for the last 5 questions,and I relise now that theyre all stupid mistakes that wouldnt have happened if I read the question more carefully... Ah well

#### farahodish

##### Member
for question 4, can someone help me out
this is what i thought
i took it as thought the original 'r' was '4r' and it went down to simply 'r' so i got option a)
how is that wrong? LOL

#### Hallatia

##### Member
I remember it was really hard and in the end I guessed a lot of them, the exact pattern for my answers went: ABCDABBB ABCDCDC

#### ballin

##### Banned
ok i think most of these are right, anyone confirm..??

1- A
2- A
3 - B (guess)
4 - D
5 - D
6 - D (guess)
7 - C
8 - A (guess)
9 - C (guess)
10 - A
11 - D
12 - B
13 - C (guess, used LHR)
14 - C
15 - D

a lot of guesses i guess, but they were the educated sort

#### flowergrl

##### Member
[FONT=바탕][FONT=바탕]1)[/FONT] [/FONT][FONT=바탕]A [/FONT]
[FONT=바탕]Clearly, the centripetal force is the gravitational force, hence it must be in the same direction.[/FONT]
[FONT=바탕][FONT=바탕]2)[/FONT] [/FONT][FONT=바탕]A) The ovserver on spaceship is the proper length (same frame of ref as the rocket). Observer on planet measures contracted length. Hence A[/FONT]
[FONT=바탕][FONT=바탕]3)[/FONT] [/FONT][FONT=바탕]B[/FONT]
[FONT=바탕]Equating KE (equivalent to work done) is equal to GMm(1/r-1/R). Thus mass and work are not correct answers. Clearly, v is NOT SPEED OF EARTH[/FONT][FONT=바탕]S ROTATION. It is the satellite[/FONT][FONT=바탕]s. Thus, it must be B (note that C is derived from KE=GPE.[/FONT]
[FONT=바탕][FONT=바탕]4)[/FONT] [/FONT][FONT=바탕]sub r= R/4 and you get D[/FONT]
[FONT=바탕][FONT=바탕]5)[/FONT] [/FONT][FONT=바탕]this is D as acceleration is only due to gravity and this acts down. Velocity is initially positive then negative as particle travels back down after traveling up.[/FONT]
[FONT=바탕][FONT=바탕]6)[/FONT] [/FONT][FONT=바탕]D. The position shown is when torque=0 thus as you know, the coil must start from max to be able to start turning. Max when coil plane is parallel to field.[/FONT]
[FONT=바탕][FONT=바탕]7)[/FONT] [/FONT][FONT=바탕]C. Since there are double time amount of wavelengths formed per unit time, speed must be doubled. D will have same period if D is true. It is clearly not A or B.[/FONT]
[FONT=바탕][FONT=바탕]8)[/FONT] [/FONT][FONT=바탕]Emf= NEGATIVE change in flux/change in time. This is equivalent to gradient. As gradients are constant, the induced emf will have constant values. At the peaks, there is undefined gradient, thus it is D. (first half of unit time is positive gradient, hence emf must be negative constant over the same length of time.)[/FONT]
[FONT=바탕][FONT=바탕]9)[/FONT] [/FONT][FONT=바탕]C. The induced current must be maximum as magnetic field used is at maximum (this will make it harder to pedal, thus called level 6)[/FONT]
[FONT=바탕][FONT=바탕]10)[/FONT] [/FONT][FONT=바탕]Interference. (a) hertz had to measure the standing waves which occurred and this will occur at destructive and constructive interference.[/FONT]
[FONT=바탕][FONT=바탕]11)[/FONT] [/FONT][FONT=바탕]100/0.001. this is D[/FONT]
[FONT=바탕][FONT=바탕]12)[/FONT] [/FONT][FONT=바탕]B. Clearly C and D are incorrect. The X-rays must penetrate the crystal in order to form an interference pattern on the screen behind it. They are not [/FONT][FONT=바탕]scattered[/FONT][FONT=바탕]- this implies random scattering of the rays.[/FONT]
[FONT=바탕][FONT=바탕]13)[/FONT] [/FONT][FONT=바탕]B. the CURRENTS act in opposite direction to electrons. Parallel currents attract and hence the electrons in the current must move same direction as outer electron.[/FONT]
[FONT=바탕][FONT=바탕]14)[/FONT] [/FONT][FONT=바탕]C. p-types are NOT positive. How can neutral atoms suddenly charge a neutral semiconductor. Note that boron has same amount of protons as neutrons (see the periodic table)- the hole is produced due to a lack of bonding. If B was correct, the pure silicon should be called p-conductor. Phosphorus is pentavalent, so will not produce holes.[/FONT]
[FONT=바탕][FONT=바탕]15)[/FONT] [/FONT][FONT=바탕]A. The energy of a proton at rest- the proton may be vibrating thus may contain energy, but we cannot determine its energy as there is no energy to compare against. (e.g. a vibrating proton is still considered stationary). Back emf works directly by conservation of energy (otherwise a positive feedback would result and the motor would spin too infinity). C and D are clearly wrong.[/FONT]

#### Caitlin2022

##### New Member
Gravity is an inverse square force meaning F=1/d^2

#### denoz

##### Member
flowergrl said:
[FONT=바탕][FONT=바탕]1)[/FONT] [/FONT][FONT=바탕]A [/FONT]
[FONT=바탕][/FONT]
[FONT=바탕][FONT=바탕]8)[/FONT] [/FONT][FONT=바탕]Emf= NEGATIVE change in flux/change in time. This is equivalent to gradient. As gradients are constant, the induced emf will have constant values. At the peaks, there is undefined gradient, thus it is D. (first half of unit time is positive gradient, hence emf must be negative constant over the same length of time.)[/FONT]
With this question, I'm wondering how this is in the syllabus as how are we supposed to know what Faraday's law is (That is if the answer of D is true). I figured it was either C or D but if its not in the syllabus how are we supposed to know the answer.

Just curious really

Last edited:

#### matorm

##### Member
flowergrl said:
[FONT=바탕][FONT=바탕]1)[/FONT] [/FONT][FONT=바탕]A [/FONT]
[FONT=바탕]Clearly, the centripetal force is the gravitational force, hence it must be in the same direction.[/FONT]
[FONT=바탕][FONT=바탕]2)[/FONT] [/FONT][FONT=바탕]A) The ovserver on spaceship is the proper length (same frame of ref as the rocket). Observer on planet measures contracted length. Hence A[/FONT]
[FONT=바탕][FONT=바탕]3)[/FONT] [/FONT][FONT=바탕]B[/FONT]
[FONT=바탕]Equating KE (equivalent to work done) is equal to GMm(1/r-1/R). Thus mass and work are not correct answers. Clearly, v is NOT SPEED OF EARTH[/FONT][FONT=바탕]S ROTATION. It is the satellite[/FONT][FONT=바탕]s. Thus, it must be B (note that C is derived from KE=GPE.[/FONT]
[FONT=바탕][FONT=바탕]4)[/FONT] [/FONT][FONT=바탕]sub r= R/4 and you get D[/FONT]
[FONT=바탕][FONT=바탕]5)[/FONT] [/FONT][FONT=바탕]this is D as acceleration is only due to gravity and this acts down. Velocity is initially positive then negative as particle travels back down after traveling up.[/FONT]
[FONT=바탕][FONT=바탕]6)[/FONT] [/FONT][FONT=바탕]D. The position shown is when torque=0 thus as you know, the coil must start from max to be able to start turning. Max when coil plane is parallel to field.[/FONT]
[FONT=바탕][FONT=바탕]7)[/FONT] [/FONT][FONT=바탕]C. Since there are double time amount of wavelengths formed per unit time, speed must be doubled. D will have same period if D is true. It is clearly not A or B.[/FONT]
[FONT=바탕][FONT=바탕]8)[/FONT] [/FONT][FONT=바탕]Emf= NEGATIVE change in flux/change in time. This is equivalent to gradient. As gradients are constant, the induced emf will have constant values. At the peaks, there is undefined gradient, thus it is D. (first half of unit time is positive gradient, hence emf must be negative constant over the same length of time.)[/FONT]
[FONT=바탕][FONT=바탕]9)[/FONT] [/FONT][FONT=바탕]C. The induced current must be maximum as magnetic field used is at maximum (this will make it harder to pedal, thus called level 6)[/FONT]
[FONT=바탕][FONT=바탕]10)[/FONT] [/FONT][FONT=바탕]Interference. (a) hertz had to measure the standing waves which occurred and this will occur at destructive and constructive interference.[/FONT]
[FONT=바탕][FONT=바탕]11)[/FONT] [/FONT][FONT=바탕]100/0.001. this is D[/FONT]
[FONT=바탕][FONT=바탕]12)[/FONT] [/FONT][FONT=바탕]B. Clearly C and D are incorrect. The X-rays must penetrate the crystal in order to form an interference pattern on the screen behind it. They are not [/FONT][FONT=바탕]scattered[/FONT][FONT=바탕]- this implies random scattering of the rays.[/FONT]
[FONT=바탕][FONT=바탕]13)[/FONT] [/FONT][FONT=바탕]B. the CURRENTS act in opposite direction to electrons. Parallel currents attract and hence the electrons in the current must move same direction as outer electron.[/FONT]
[FONT=바탕][FONT=바탕]14)[/FONT] [/FONT][FONT=바탕]C. p-types are NOT positive. How can neutral atoms suddenly charge a neutral semiconductor. Note that boron has same amount of protons as neutrons (see the periodic table)- the hole is produced due to a lack of bonding. If B was correct, the pure silicon should be called p-conductor. Phosphorus is pentavalent, so will not produce holes.[/FONT]
[FONT=바탕][FONT=바탕]15)[/FONT] [/FONT][FONT=바탕]A. The energy of a proton at rest- the proton may be vibrating thus may contain energy, but we cannot determine its energy as there is no energy to compare against. (e.g. a vibrating proton is still considered stationary). Back emf works directly by conservation of energy (otherwise a positive feedback would result and the motor would spin too infinity). C and D are clearly wrong.[/FONT]

I believe ur all correct there except for 13....

The answer is C

----------->------ (Let this be the wire)(conv. current to right in this example)
* ( * = electron)
If we (just pick a direction as it works for both) say the current in the wire is going to the right, the magnetic field surrounding the wire is acting into the page/screen at the point of the electron (using right hand grip rule)...

We know that the force is in the same direction of current, therefore using the right hand push rule, the palm of the hand is in the direction of current (i.e. facing right), and the fingers point into the page/screen as per the magnetic field...

The thumb now shows the direction of current for a positive charge (which is pointing away from the wire), hence as a negative charge is in the opposite direction, the electron is moving towards the wire and perpendicular to it.....

This process derives the same result even if we take the conventional current moving to the left instead of the right....

Hence the answer is C....

G

#### gaoOO

##### Guest
13 is C (going by my bad physics)

i said 12 was A, but that's probably wrong, and otherwise, i agree with all of flowergrl's answers.