Frequent Mistakes Flashcards by Emma Djabali

What is the equation for the maximum KE of an electron in the photoelectric effect?

Kmax = hf - W

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What is the work function What does it represent?

W = h.ft

ft= threshold frequency
It’s the minimum energy required to eject an electron

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What is the equation for exponential decay?

n = no . e ^(-lambda.t)

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What is the equation for the rate of exponential decay? What about the decay constant?

Delta n/Delta t = - lambda . n

n= number that remains
Lambda = decay constant = 0.7/T1/2

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Area of a sphere?

4.pi.r^2

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Volume of a sphere?

4/3.pi.r^3

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Area of a circle?

pi. r^2

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Equation for Beta negative decay?

X –> (Z+1) Y + Beta -

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Equation for Beta positive decay?

X –> (Z-1) Y + Beta +

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What is ln (1)?

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What is ln(x) when x

negative

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What is ln(x) when x>0?

Positive

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What are the steps to solve conservation of energy problems?

Write an expression for initial energy E = U + K
If there is friction, air resistance, or drag, the difference between Ei and Ef is the energy lost due to those
If there isn’t any of those than Ei = Ef
Solve for the quantity of interest

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How do you calculate the percentage energy lost?

Ef/Ei x 100

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How to find the horizontal velocity of an object thrown at an angle?

Use x = v/t

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How to find the initial velocity of an object thrown at an angle and landing further?

Find the original velocity with x = v/t

2. Then use trig!

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What do to when asked to determine which object will reach the ground first when thrown at different angles and velocities?

Compare the initial vertical velocity! The highest one will hit the ground last.

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What is the force that holds 2 objects together when they are being slided against each other?

Force of friction

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How to calculate the net displacement when an object is moving in 3 perpendicular directions?

= squaroot of (x^2 + y^2 + z^2)

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Can the acceleration be (+) even at constant velocity?

Yes! Because the direction could be changing

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How to calculate the displacement when given a graph of velocity vs time?

Calculate the area between graph and x axis

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What is necessary to be able to lift an object?

The force applied must be greater than the force of gravity

Is the velocity of an object being dropped dependent on its weight?

No, only depends on surface area because of friction

When can I say that the object is not experiencing a net torque?

When it isn’t in rotational motion

What happens to one's velocity when someone jumps off something?

If someone/thing jumps and hits the ground, his acceleration will be pretty constant for a while, then decrease (but not reach 0), and finally go back up (gravity!)

How to calculate the mass of an object when in equilibrium and a mass hanging from one side?

Use torques and the center of mass

If 2 objects of different mass are sitting on a spring and the spring propels them up, will one object be propelled higher than the other?

How can I know how far an object will be propelled by a spring?

1/2 k. x^2 = mgh

What does using a pulley change? What does it not?

It changes the force necessary, not the amount of work! n

What is the purpose of ideal and non ideal machines?

Reduce the force required

What is the difference between ideal and non ideal machines?

Non ideal machines increase to word required

What is the equation I should use for levers?

F1 . L1 = F2 . L2

What is the equation I should use for work done by machines?

Finput . d input = Foutput . d output

Resistors experience the same current when they are in?

Series!

Resistors experience the same voltage when they are in?

Parallel!

In the doppler effect equation, which v is on top?

D!!!

During echolocation, what is considered the detector and what is considered the source?

Both are the animal using echolocation

When we look at things in water, do we see them closer or further than they actually are? Why?

Further, because we see the light as straight, and we do not account for bending of the light

What does transmutation mean in nuclear reactions?

Radioactive decay resulting in a change of atomic number; special type of fission

What are newtons in SI units?

kg . m / s^2

When object are thrown vertically and you are given vo, what does the value represent?

The horizontal velocity

How to calculate average acceleration when the direction changes?

Assign each velocity vector a sign. To the right can be positive, to the left can be negative.

Is kinetic energy related to velocity or speed?

Speed

What are Newtons in terms of Joules?

J/m

What is happening in translational equilibrium?

There is an equal amount of work done by the forces

When is the kinetic energy of a substance 0?

At absolute 0 (temp)

Main difference between convection and conduction?

Conduction usually happens through solids with contact, and convection through the bulk movement of fluids: mixing of both objects in the system

What is radiation?

Heat transfer through electromagnetic waves

1 C = ? F

1.8 F

What does (+) work mean?

Work is being done by system (expansion)

What does (-) mean?

Work is being done on system (compression)

What graph will have an area equal to work?

P-V graph

What is the second law of thermodynamics? What does it have to do with?

Objects will transfer heat until they reach thermal equilibrium → entropy : energy spontaneously disperses!