L1
Neutrons and protons have same mass. True or False?
False.
Electrostatic force between two charges is proportional to what function of radius?
Inverse square.
State Law of Conservation of Momentum, for two colliding objects.
m1u1 + m2u2 = m1v1 + m2v2
v = ?
f*lambda
I place a q=+10^6 C point charge 10m away from a neutral object. What is the force the charge exerts on the neutral object?
0.
They lose electrons until they have less e- than p+.
List two units used to express Electric Field Strength.
Volts/meter, Newtons/Coulomb.
In equations, P represents ___ with units ___, whereas p represents ___ with units ___.
P: Power, in Watts (W)
p: Momentum, in Kilogram Metres per Second (kgm/s)
Two square waves (+2cm, +3cm sides, i.e. both have positive displacement) approach each other. What do they look like superimposed?
Square snowman 5cm high by 3cm wide (2cm wide top).
A thundercloud floating 1km above the Earth models a set of parallel plates, with electric field strength 1N/C.
What is the voltage at 500m altitude?
V_max = Ed = 1*1000 = 1000V
V_500 = s/d* V_max = 500/1000 * 1000 = 500V
Draw full theoretical electric field diagram around parallel plates, including fringe effects.
Uniform E. field btwn. (equal spacing, straight lines w/ 90deg angle), bevel outward at edges, beveling wraps around to back also. Arrows point pos. -> neg.
Differentiate Electric Potential Energy and Potential Difference.
EPE -- Energy a charge has due to position within E field.
PD/Voltage -- Energy per unit charge expended by/given to objects travelling from point A to B in an electric field.
My Uber driver has a pet wasp inside their car. They insist it's safe because the car always cruises at 60km/h whereas wasps fly at 30km/h max, and hence it will be stuck to the back window.
Will the driver get stung? Why/Why not?
Will get stung. At constant vel., car contents go at same speed. Wasp flies relative to air, but there is no relative motion between car and air inside car. Hence, when wasp flies freely within/relative to car.
Law of Conservation of Energy. (Heat is transferred thermal energy, where lost is gained elsewhere)
The Incredible Bulk throws 100kg cannonballs (towards the horizon of Earth) charged at +98C in electric field of 10Vm^-1 up.
Assuming electric field is infinite, how far does the cannonball fly?
F_net (upward) = F_E - F_g = Eq - mg
Assuming g stays 9.8:
= 10*98 - 100*9.8 = 0
Hence no net force, accel. therefore should fly infinitely.
Describe the electric field between a dipole in 3D.
Like mandarin bud pattern extending outward to infinity, except for single straight lines on opposite sides. Arrows point pos. -> neg. pole.
Middle-aged men in their mid-life crisis bet on whether beta- (e-), or alpha (2p+, 2n) particles will travel the fastest in an electric field.
If you were a middle-aged man, what would you bet on and why?
Electron/Beta-. Much smaller mass = much larger acceleration --> travels the fastest.
Name 5 kinematic equations.
s=ut+1/2*at^2, v^2=u^2+2as, v_av=s/t, a=delta(v)/delta(t), s=1/2*(u+v)t, etc. etc.
A half-blind old man got scammed into buying a flat magnifying glass.
However, he notices if he sticks text right up against it, it seemingly moves to a different place and closer to the top of the glass.
Eyes think light travels straight, but refraction has traced a non-straight path --> displaced text (just like chopsticks in water).
Tracing true distance into the perceived angle (straight line), text appears closer to top of glass.
70kg playboy billionaire Bony Bark tries to make a flying suit by plating his floor and ceiling (10m high) with metal plates at 100V potential difference.
He's planning on wearing 30kg charged metal plates to help him fly. What's the minimum charge magnitude he should use?
mg = F = Eq = V/d*q
q = mgd/V = (70+30)*9.8*10/100
q = 98C
Explain the three methods of charging.
Contact/Conduction -- Diff. charged conductors will reach equilibrium (uniform charge spacing) when connected.
Friction -- Some number of e- rubs off from one insulator onto another, where they stay stuck until relocated.
Induction -- Charged object induces charge separation in conductor. When conductor is separated into two pieces, separated charges cannot reunite --> charged objs.
Draw fully labelled equipotential line set, including outside effects, around parallel plates.
Oblong rings around each plate (always perp. to E field). Between plates is parallel and equidistant. Voltage low around the neg. plate, high around pos. plate.
1. Law of Inertia -- Objects at rest/const. vel. will stay so.
2. Law of Accel. -- F=m*a
3. Law of Re/Action -- Two interacting bodies apply forces with equal magnitude but opposite direction onto one another. F_AB = - F_BA
Given a displacement-time graph of a sound wave, name 4 variables you can derive.
Amplitude, Period --> Frequency --> Wavelength (knowing v=340ms^-1)
I'm making an electric peashooter. I rub my 2 gram peas against my shirt to give them 0.002C, before putting them in my 25cm tube with 2NC^-1
What speed do they exit the tube at, if I aim horizontally?
qEd = W = 1/2*m*v^2
v^2 = 2qEd/m = 2*0.002*2*0.25/0.002 = 1
v=1ms^-1