Modern Physics

Two clocks are synchronized on a space station. One clock is placed on a spaceship that moves close to the speed of light relative to the space station. Which of the following is true:

• Time is moving at a faster rate for the moving clock as viewed from the reference frame of the stationary clock.

• Time is moving at a slower rate for the moving clock as viewed from the reference frame of the stationary clock.

• Time is moving at a slower rate for the stationary clock as viewed from the reference frame of the moving clock.

An astronaut travels in a spaceship at a velocity close to the speed of light and returns to Earth. Which of the following statements is correct regarding the astronaut's age compared to people who stayed on Earth?

• The astronaut will be older than those who stayed on Earth.

• The astronaut will be younger than those who stayed on Earth.

• The astronaut and those on Earth will be the same age.

Einstein is on a windowless train and running late to a meeting, so he wants to know if the train is moving. He holds up a mirror and shines a laser into it, noticing that the light seems to leave the laser, hit the mirror, and reflect directly back to him. Based on this information:

• Einstein can tell that he is in a moving reference frame (the train is moving).

• Einstein can tell that he is in a stationary reference frame (the train is not moving).

• Einstein cannot tell whether the train is moving or not.

A distant star is 9 lightyears away as measured in the Earth's reference frame. A spaceship is launched towards this star and travels at a constant speed. Observers on Earth measure that the spaceship takes 10 years to get there. Which of the following describes what is observed from the spaceship's reference frame?

• The astronauts observe the trip taking less than 10 years because of time dilation, and they also observe the distance to the star to be shorter due to length contraction.

• The astronauts observe the trip taking more than 10 years due to time dilation, and they observe the distance to the star to be longer due to length expansion.

• The astronauts observe the trip taking less than 10 years because of time dilation, but the distance to the star remains 9 light-years.

• The astronauts observe the trip taking 10 years, and the distance to the star remains 9 light-years.

Black holes are extremely dense objects that absorb incoming light and matter. Black holes can emit a very specific type of radiation, and have a non-zero temperature. True or false: black holes are an example of a black body.

• True
• False

In the photoelectric effect, light of a certain frequency strikes a metal surface and causes electrons to be emitted. Increasing the intensity of the light will cause more electrons to be emitted. Why does this happen?

• Increasing the intensity increases the energy of each photon, allowing them to release more energetic electrons.

• Increasing the intensity increases the number of photons which strike the surface, causing more electrons to be emitted.

• Increasing the intensity increases the work function of the metal, allowing more electrons to be ejected.

I can measure the momentum of my car and also tell precisely where it is. This seems inconsistent with Heisenberg's uncertainty principle. How can I explain this?

• Advanced equipment allows us to to accurately measure both position and momentum at larger scales.

• Large objects behave according to classical physics, so the uncertainty principle does not apply.

• The uncertainty principle only applies to fundamental particles. It is not true for constructed objects.

• The uncertainty principle still applies to large objects, but the uncertainties are so small that they are undetectable.

Wave-particle duality tells us that:

• Light behaves as a wave.

• Light behaves as a particle.

• Light behaves as a wave and a particle.

• Light behaves as a wave or a particle, depending on the situation.

If Planck's constant was 10³⁴ times larger than it really is, what would be the effect on our observations of the universe?

• Quantum effects like quantization of energy would be measurable at every day scales. For example, a swing would only be observed to reach certain discrete heights instead of a continuum of heights.

• Quantum effects like quantization of energy would be measurable at every day scales. However, since we already see these effects at every day scales, we would not observe any differences in every day life.

• No matter the value of Planck's constant, quantum effects would not be measurable at every day scales.

An experiment is set up so that an electron can travel through two different paths- path A or path B- to reach a detector. No measurement is made to check which path the electron takes. Which of the following options describes what happens with the electron.

• The electron travels only through path A, but is able to affect path B.

• The electron chooses randomly which path to travel through.

• The electron travels through both path A and path B at the same time.

• The electron appears at the detector without having taken either path.