Paper 3: General and Practical Principles in Physics

Describe how to measure g using an electromagnet, a steel ball and a light gate or trapdoor timer.

Figure 1 shows h against t². Use it to determine g.

Explain why electronic timing is better than a stopwatch here, and why the largest heights give the most reliable results.

Describe how to investigate how the pressure of a fixed mass of gas at constant volume varies with temperature.

Figure 2 shows the results. Use the data to estimate absolute zero.

Explain why the tubing connecting the flask to the pressure gauge should be as short as possible.

Describe how a top-pan balance can be used to determine the magnetic flux density between two magnets.

The gradient of a graph of balance reading (g) against current (A) is 2.45 g A⁻¹. The length of wire in the field is 0.050 m. Calculate B and explain why the balance reading can increase.

Describe how to investigate how the period of a mass–spring system depends on the mass.

The gradient of T² against m is 0.158 s² kg⁻¹. Calculate the spring constant and explain why the line does not pass through the origin.

An electric car's battery stores 60 kWh. Convert this to joules.

At a steady 25 m s⁻¹ the total resistive force is 600 N. The motor system is 90% efficient. Calculate the range of the car at this speed.

Explain how regenerative braking uses electromagnetic induction to recharge the battery.

The car is charged at 400 V and 125 A. Calculate the time to fully charge the battery and explain why the charging cables are thick.

Sodium-23 ions (charge +e, mass 3.82 × 10⁻²⁶ kg) are accelerated through 1500 V and enter a 0.25 T magnetic field at right angles. Calculate their speed and the radius of their path.

Before the magnetic field, ions pass through a velocity selector with crossed electric and magnetic fields. Explain how it works and calculate the electric field needed for these ions if B = 0.25 T.

Explain how the spectrometer separates isotopes of the same element.

In the Sun, 4 ¹H → ⁴He + 2e⁺ + 2ν. Mass of ¹H nucleus 1.007276 u, ⁴He nucleus 4.001506 u, positron 0.000549 u. Calculate the energy released in MeV (1 u = 931.5 MeV).

The Sun's luminosity is 3.83 × 10²⁶ W. Calculate the mass it loses each second, and explain why fusion happens only in the core.

The Sun's spectrum peaks at 502 nm. Calculate its surface temperature and use the luminosity to calculate its radius.

Calculate the intensity of sunlight at the Earth's distance (1.50 × 10¹¹ m).

Light of intensity 800 W m⁻² falls on a 1.6 m² solar panel that is 20% efficient. Calculate the electrical power output and the number of photons hitting the panel each second, assuming all have wavelength 550 nm.

Explain why polarising sunglasses reduce glare from a wet road.

A 70 kg bungee jumper falls 20 m before the cord becomes taut. The cord has stiffness 180 N m⁻¹. Calculate the maximum extension of the cord.

Calculate the jumper's acceleration at the lowest point.

Calculate the period of the jumper's oscillations on the cord and explain why the oscillations die away.

The International Space Station orbits 410 km above the Earth's surface (Earth radius 6.37 × 10⁶ m, mass 5.97 × 10²⁴ kg). Calculate its orbital speed and period.

Explain why astronauts on the ISS feel weightless even though g there is about 8.7 N kg⁻¹.

Discuss what astronomers know about the age and fate of the Universe, and why there is uncertainty.

Describe how to measure the speed of sound in air using a signal generator, loudspeaker, two microphones and an oscilloscope.

At 2.0 kHz the microphone was moved 0.86 m while the traces came back into phase five times. Calculate the speed of sound.

The distance was measured to ±0.005 m. Calculate the percentage uncertainty in v from this and explain why measuring over five wavelengths is better than one.

Describe how to determine the wavelength of laser light using a diffraction grating.

A grating with 300 lines per mm is 1.50 m from a screen. The two second-order maxima are 1.20 m apart. Calculate the wavelength.

Give one safety precaution and explain why using higher orders improves accuracy.