IB Physics SL Theme D: Fields questions

Exam-style multiple choice and written questions with full markschemes. Check multiple choice answers straight away, or type, photograph or draw a written answer and get it marked.

Type
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Question 1

Paper 2Medium12 marks

A probe is outside a spherical asteroid of uniform density. The asteroid has radius 4.0×105 m4.0\times10^5\ \mathrm{m} The probe has mass 800 kg800\ \mathrm{kg} Figure 1 shows the meaning of rr and measured values of the gravitational force FF on the probe at different distances from the asteroid’s centre.

ORPrMeasured gravitational force on the probe4567891002468101214r/(105 m)F/N

The gravitational constant is G=6.67×10−11 N m2 kg−2G=6.67\times10^{-11}\ \mathrm{N\,m^2\,kg^{-2}}

(a)

State how the asteroid’s mass is treated when calculating the gravitational force on the probe.

[1]
(b)

Use Figure 1 to state the measured gravitational force when r=6.0×105 mr=6.0\times10^5\ \mathrm{m}

[1]
(c)

Use this measurement to estimate the mass of the asteroid.

[3]
(d)

Using your estimate from (c), calculate the gravitational force on the 800 kg800\ \mathrm{kg} probe when r=8.0×105 mr=8.0\times10^5\ \mathrm{m} State whether this result agrees with Figure 1.

[3]
(e)

At r=8.0×105 mr=8.0\times10^5\ \mathrm{m} a second probe has a mass of 1.6×103 kg1.6\times10^3\ \mathrm{kg} Determine the gravitational force on this probe.

[2]
(f)

A student suggests that the readings at r=6.0×105 mr=6.0\times10^5\ \mathrm{m} and r=8.0×105 mr=8.0\times10^5\ \mathrm{m} are consistent with F∝1/rF\propto 1/r Use these readings to assess the suggestion.

[2]

Question 2

Paper 2Medium4 marks

During a Millikan-type investigation, the charge magnitudes of positively charged oil droplets are measured. Droplets A and B coalesce to form droplet C. No charge is transferred to or from the surroundings during coalescence. Figure 1 also shows measurements for droplets D and E. Each plotted measurement has an uncertainty of ±0.1 in the units shown.

ABCDE0123456789DropletMeasured charge magnitude, q / (10⁻¹⁹ C)3.24.78.01.66.3
(a)

Use Figure 1 to estimate the elementary charge and explain how the measurements provide evidence that electric charge is quantized.

[2]
(b)

Using your estimate in (a), assess whether the coalescence of A and B is consistent with conservation of electric charge.

[2]

Question 3

Paper 2Medium8 marks

An electron enters the region between two parallel plates as shown in Figure 1. The electric field between the plates is uniform. Ignore edge effects and the gravitational force on the electron. The electron has no initial vertical velocity.

+−e−vx = 2.0 × 107 m s−1400 V6.0 cm4.0 cm

The magnitude of the electron’s charge is 1.60×10−19 C1.60\times10^{-19}\ \mathrm{C} and its mass is 9.11×10−31 kg9.11\times10^{-31}\ \mathrm{kg}

(a)

State the direction of the electric force on the electron.

[1]
(b)

Calculate the magnitude of the electric field between the plates.

[1]
(c)

Calculate the magnitude of the electron’s acceleration between the plates.

[2]
(d)

Determine the vertical displacement of the electron from its entry point when it reaches the right end of the plates.

[3]
(e)

Determine the vertical component of the electron’s velocity at the instant it reaches the right end of the plates.

[1]

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