Expert TA provides more than just hints on problems. Our specific feedback is sophisticated and in direct response to the error or errors the student has made.

Our ability to recognize mathematical equivalents means that students receive that feedback regardless of the format of their answer. This is helpful both during the assignment and afterward in the grade report.

## Seeing is Believing

Explore hints and feedback in Expert TA.

Explore DemoHere are several examples of actual feedback accessed by Expert TA users in Physics I and II classes.

## Mechanics and Heat (Physics I)

**Example 1**

CORRECT ANSWER: 2v_{0}sin(ϴ)/g

STUDENT’S INCORRECT ANSWER: v_{0} sin(ϴ) / g

FEEDBACK: “This is the time it takes for a ball to reach maximum height. The question is about total time of flight.”

**Example 2**

CORRECT ANSWER: Dcos(ϴ)i + Dsin(ϴ)j

STUDENT’S INCORRECT ANSWER: sin(ϴ)D + cos(ϴ)D

FEEDBACK: “This is just a sum of components. You should give the answer in vector form. Use unit vectors i and j.”

**Example 3**

CORRECT ANSWER: Dcos(ϴ)i + Dsin(ϴ)j

STUDENT’S INCORRECT ANSWER: sin(ϴ)j + cos(ϴ)iD

FEEDBACK: “Your equation has the wrong dimensions.”

**Example 4**

CORRECT ANSWER: ( T – g m_{2} ) / m_{2}

STUDENT’S INCORRECT ANSWER: T / m_{2}

FEEDBACK: “You have forgotten to include the weight of m_{2}.”

**Example 5**

CORRECT ANSWER: – μ_{kg}

STUDENT’S INCORRECT ANSWER: μ_{kg}

FEEDBACK: “Acceleration and the net force always have the same direction. Check the sign of your answer.”

**Example 6**

CORRECT ANSWER: F_{N} – mg

STUDENT’S INCORRECT ANSWER: mg + F_{N}

FEEDBACK: “Check your free body diagram; normal force is in the opposite direction to the force of gravity.”

**Example 7**

CORRECT ANSWER: F_{2}sin(ϴ) + mg

STUDENT’S INCORRECT ANSWER: F_{2}sin(ϴ)

FEEDBACK: “You have neglected to include the weight.”

**Example 8**

CORRECT ANSWER: Fcos(ϴ)d

STUDENT’S INCORRECT ANSWER: Fd

FEEDBACK: “You only need the component of the force that acts in the direction of motion. Which trigonometric function, sine or cosine, is needed?”

**Example 9**

CORRECT ANSWER: Fcos(ϴ)d

STUDENT’S INCORRECT ANSWER: Fcos(ϴ)

FEEDBACK: “Work is equal to a force multiplied by a distance. You have only included the force.”

**Example 10**

CORRECT ANSWER: v_{0}cos(ϴ)i + v_{0}sin(ϴ)j

STUDENT’S INCORRECT ANSWER: v_{0}cos(ϴ) + v_{0}sin(ϴ)

FEEDBACK: “You are missing your unit vectors i and j. As written, you are adding the x and y components of the velocity, which you can’t do.”

**Example 11**

CORRECT ANSWER: P / m

STUDENT’S INCORRECT ANSWER: m / P

FEEDBACK: “You may have made an algebraic mistake. This is the inverse of the velocity.”

## Electricity and Magnetism (Physics II)

**Example 12**

CORRECT ANSWER: 0

STUDENT’S INCORRECT ANSWER: L_{2}IB

FEEDBACK: “Current in L_2 is parallel or anti-parallel to magnetic field lines. Force should be equal to 0.”

**Example 13**

CORRECT ANSWER: μ_{0}I_{1}I_{2}ln(2)/(2π)

STUDENT’S INCORRECT ANSWER: μ_{0}I_{1}I_{2}/(2π)

FEEDBACK: “The magnetic force is not constant. You should integrate to find the result.”

**Example 14**

CORRECT ANSWER: μ_{0}I_{1}I_{2}b/((2π(d + a)))

STUDENT’S INCORRECT ANSWER: μ_{0}I_{1}I_{2}b/((2π(d – a)))

FEEDBACK: “Given the denominator 2πd – 2πa: You have a sign error in this term.”

**Example 15**

CORRECT ANSWER: -BLv∆t

STUDENT’S INCORRECT ANSWER: BvL∆t

FEEDBACK: “Flux through loop 2 is decreasing; it means change is negative.”

**Example 16**

CORRECT ANSWER: λ/n_{o}

STUDENT’S INCORRECT ANSWER: λn_{o}

FEEDBACK: “The wavelength should be shorter in the oil, not longer.”

**Example 17**

CORRECT ANSWER: λ/(2n_{o})

STUDENT’S INCORRECT ANSWER: (2n_{o})/λ

FEEDBACK: “This is the inverse of t.”

**Example 18**

CORRECT ANSWER: ε_{0}c_{2}/c_{1}

STUDENT’S INCORRECT ANSWER: c_{2}/c_{1}

FEEDBACK: “This is the dielectric constant of oil – the question is about permittivity.”