**Results from AP Exams**

*Jiang Yu, Chief Reader*

*I attended this session to gain some insights into how the AP Physics B exam is scored and what common mistakes students made on the exam.*

* Question B1
* 6.6/10
* common errors
* omit one of the three forces or add a normal force on FBD
* use unconventional labels for their forces
* units! students often omitted units
* not recognize buoyancy is measured in Newtons
* forces that appeared on the FBD often did not match the ones appeared in subsequent calculations
* not using physics but general language in justification
* Question B2
* 6.0/15
* common errors
* applied kinematic equations for constantly accelerated motion to a motion of changing acceleration
* not recognize that W=Fd can only be used when F is constant
* not knowing that spring force is not a constant force
* explanations are not concise and clear
* Question B3
* 3.6/10
* common errors
* non-linear scaling of axes in graphing
* best-fit line often is drawn by just connecting points
* not showing work for calculating slope of the best-fit line
* not understanding that the light must pass from a higher index of refraction to a lower index of refraction in order to have total internal reflection
* Question B4
* 3.6/10
* common errors
* not reading the question carefully and not answering what is asked
* not showing enough work beginning with the correct equations and then all the needed steps leading to an answer
* messing up the horizontal and the vertical dimensions in calculations
* deficiency in understanding the conservation of momentum
* using “energy,” “force,” “momentum” and “velocity” interchangeable in explanations
* Question B5
* 3.6/10
* common errors
* misunderstanding of the sign conventions in evolved for heat, work and energy
* not clear with their justifications, but often simply restated the question, and answer without providing further support
* connected heat or average kinetic energy to temperature, but not to the internal energy
* used W = -PΔV and did not discuss the effect of temperature on the pressure
* Question 6
* 3.5/15
* common errors
* simple calculations errors were everywhere
* incorrect use or value of the magnetic permeability, μo, in Ampere’s Law
* not understanding the intent of parts (a) & (b)
* did not clearly understand the nature of the question and the connection of the parts to each other
* Question 7
* 2.7/10
* common errors
* the most common errors were the result of a lack of understanding of atomic states and associated energy levels. Students seemed to choose and use the equations without basic understanding of the physics involved.