The intensity of a wave can be defined as the energy per unit area per unit time. What is the unit of intensity expressed in fundamental SI units?

A.  kg m⁻²s⁻¹

B.  kg m²s⁻³

C.  kg s⁻²

D.  kg s⁻³

D

The unit analysis in this question proved tricky for many HL candidates, with option A being the most common (incorrect) answer. The high discrimination index suggests that this question was more problematic for weaker candidates.

A student is verifying the equation

$$x=\frac{2\lambda Y}{z}$$

The percentage uncertainties are:

What is the percentage uncertainty in x?

A. 5 %

B. 15 %

C. 25 %

D. 30 %

B

This question was well answered by candidates, as shown by a high difficulty index.

Four particles, two of charge +Q and two of charge −Q, are positioned on the $x$-axis as shown. A particle P with a positive charge is placed on the $y$-axis. What is the direction of the net electrostatic force on this particle?

D

The uncertainty in reading a laboratory thermometer is 0.5 °C. The temperature of a liquid falls from 20 °C to 10 °C as measured by the thermometer. What is the percentage uncertainty in the change in temperature?

A.  2.5 %

B.  5 %

C.  7.5 %

D.  10 %

D

Many candidates failed to recognize that the uncertainty in this error propagation question would affect both the initial and final temperature readings. The most common answer (option B) was incorrect, and only a minority of students correctly selected option D.

What is a correct value for the charge on an electron?

A. 1.60 x 10^–12 μC

B. 1.60 x 10^–15 mC

C. 1.60 x 10^–22 kC

D. 1.60 x 10^–24 MC

C

Which is a correct unit for gravitational potential?

A. m²s⁻²

B. J kg

C. m s⁻²

D. N m⁻¹kg⁻¹

A

A proton has momentum 10^-20 N s and the uncertainty in the position of the proton is 10^-10 m. What is the minimum fractional uncertainty in the momentum of this proton?

A. 5 × 10^-25

B. 5 × 10^-15

C. 5 × 10^-5

D. 2 × 10⁴

C

Over 100 candidates left this blank. It is testing fractional uncertainty and also involves the Heisenberg uncertainty principle.