# Search results

1. ### What directions do the current and electric field point if the electrons move right?

Yes, the electric field is to the left, in the same direction as the positive charges move. You can apply an external electric field perpendicular to a beam of electrons, for example, if you want to deflect them. This is exactly what is done in an oscilloscope to deflect the beam of electrons...

3. ### What directions do the current and electric field point if the electrons move right?

The RHR is for finding the direction of magnetic fields. If electrons move to the right then conventional current, which is a flow of positive charge, moves to the left. The direction of the electric field is the direction of the force on a positive charge. That is, in this case, the direction...
4. ### Damped oscillator consecutive amplitude ratio

This is useful http://en.wikipedia.org/wiki/Logarithmic_decrement
5. ### When you can't use conservation of energy

Indeed. I could have added that in questions of this type, it's whether or not you can consider mechanical energy to be conserved.
6. ### When you can't use conservation of energy

It depends what you have done. If you can show us how you attempted to solve the problem it would help. The exact wording of the question is also important. Questions like this usually say things like "ignore friction" as a clue to being able to use conservation of energy. Energy can take a...
7. ### Varying pressures

Yes that's correct.

9. ### Effective Resistance if bent in the form a circle

It's because it is equivalent to having two resistors in parallel. The current entering at A has a choice of 2 directions. Both involve taking a path that is 4R. That is, half the resistance of the complete wire. (Round half the circumference to B.) So to find the combined resistance, you need...
10. ### Proving Optical Law in plane mirror

You have actually already proved it. You have proved that the image of point A is at the point marked a and that this point is -behind the mirror -equidistant -in the position shown Now do the same for any other point on the object and you will find the same result. All points on the object...
11. ### Size of cavity on expansion

Imagine a circular metal plate on which you have drawn a chalk circle about half way between the centre and the rim. Heat the plate. Does the chalk circle expand or contract? Now cut out a hole in the plate marked out by the chalk but with the chalk line just visible. Heat the plate. Does the...
12. ### Grounding/earthing in a simple circuit

Yes. The potential of the left side of the circuit will be +0.5V and the potential of the right side of the circuit will be -0.5V This gives a potential difference of 0.5V - (-0.5V) = 1V
13. ### Grounding/earthing in a simple circuit

No it doesn't affect the voltage drop (pd) across the two resistors. What it does do is to set the potential of the point between the two resistors at zero. To the left of the left R the potential will be positive and to the right of the right R the potential will be negative.
14. ### Augustine in septic tank (Alice in Wonderland)

Yes that's fine now.
15. ### Orbit of Moon and the earth around thier COM

The moon's orbit is not regular. There is a perigee and apogee whereby the distance between the Earth and Moon varies considerably during its orbit. This in turn means the distance of both Earth and Moon from the CoM varies. The c of m is in orbit about the Sun which gives rise to a slight...
16. ### Vibrations of a circular membrane

J0,1 top left, corresponds to (0,1) J0,2 corresponds to (0,2) - not shown J0,3 corresponds to (0,3) - third along second row and so on... Not all all the figures in the upper set of diagrams are represented in the lower set, and vice versa. This is what is confusing.
17. ### Conflict normal force in inclined plane

The vertical component of N equals mg as there is no vertical motion. The horizontal component of N equals the centripetal force. Combine these two and eliminate N and m Obtain a formula relating the angle to v r and g
18. ### Conflict normal force in inclined plane

There is no component of gravity pointing towards the centre. It's the component of the normal reaction force from the track that points towards the centre, and in doing so provides the centripetal force for the circular motion.
19. ### Augustine in septic tank (Alice in Wonderland)

a) the vertical falling motion is independent of the horizontal, so there is no need to include the horizontal velocity in this. (Where does the angle 270 come from, by the way?) The initial vertical velocity is zero in this formula. b) correct c) you need to use the correct answer for a) for...
20. ### Heat and temperature change in liquid

The heat lost by portion A plus the heat lost by portion B equals the heat gained by portion C if the final temperature is 50 deg C Write this down as an equation in terms of m, c and the change in temperature for each portion. Rearrange/solve for mC

22. ### Why do we apply sign conventions to optics formulae?

If you use the Real is Positive sign convention, the formula for all lenses and mirrors is 1/v + 1/u = 1/f There is no minus sign. You then assign a positive value to any distance to a real image or object. You assign a negative value to virtual image or object distances. You assign a positive...
23. ### Simple centripetal force question

I beg to differ. If the disk has constant rotational speed there is no tangential force needed on the rock. The rock is moving at constant speed in a circle, and as such requires a centripetal force. This force is provided by the friction between the disk and the rock. It's direction is always...
24. ### Doppler Effect + Wavelength problem! Help Please

If the source is not moving the waves are unchanged and their wavelength is simply given by v/f where v is their speed in still air and f the original frequency. The frequency of the sound heard by the moving listener is higher because he passes through the approaching waves at a higher rate...
25. ### Lab Problems with Simple Harmonic Motion in Springs

50 gram is 0.05kg not 0.5 kg There is the factor of 10 you have lost in the calculation of the slope. The slope, k, is force divided by extension. This is Newton divided by meter
26. ### Lab Problems with Simple Harmonic Motion in Springs

I calculate a different value for the slope. Have you remembered to -make sure the mass is in kg -multiply mass by g to calculate the force? The value of k must be in units of Nm-1 Your answer being out by a factor of about 10 is the clue.

Perfect :)
28. ### Impulse Multiple choice question

Impulse is the force multiplied by the time for which that force acts. In this case, what can you say about the force of object 1 on 2 and object 2 on 1? What can you say about the time for which these 2 forces act? In conclusion, what can you say about the 2 impulses?
29. ### Frequency of a wave?

Period is the time for ONE cycle. You are given the time for 20 cycles. Can you find the time for one? You know the relationship between period and frequency.
30. ### Conservation of Momentum Homework Help

Can you show your attempt at this question and what formula(s) you think you will need.