In the moving frame $K'$ (moving with velocity $+v$ in the $x$ direction), we make a measurement that an object is at a location $x_0'$, what is the location $x_0$ of the object in the rest frame $K$? Use the Galilean transformation for now. 1. $x_0 = x_0' + vt$ 2. $x_0 = x_0' - vt$ 3. I'm confused _Hint: Yours truly got it wrong yesterday!_ Note: * Correct Answer: A
<img src="./images/lucy_and_ricky_1.png" align="center" style="width: 500px";/> Two firecrackers explode. Lucy, halfway between the firecrackers, sees them explode at the same time. Ricky (same reference frame as Lucy) is next to firecracker 2. According to Ricky, which firecracker explodes first? 1. Both explode at the same time 2. Firecracker 1 explodes first 3. Firecracker 2 explodes first *Hint: Separate what Ricky "sees" from what he would observe.* Note: * Correct Answer: A
<img src="./images/light_clock.png" align="center" style="width: 700px";/> In which frame of reference is the time between tics of the clock **longer**? 1. Rest frame of clock 2. moving frame 3. no difference Note: * Correct Answer: B
<img src="./images/light_clock.png" align="center" style="width: 700px";/> What is the **minimum** number of observers needed in the **rest frame** to measure the "tic"? 1. 1 2. 2 3. 3 4. More than 3 5. ??? Note: * Correct Answer: A
<img src="./images/light_clock.png" align="center" style="width: 700px";/> What is the **minimum** number of observers needed in the **moving frame** to measure the "tic"? 1. 1 2. 2 3. 3 4. More than 3 5. ??? Note: * Correct Answer: B
I have a stick of length $L$ sitting in front of me. In the reference frame of a passing train, (moving parallel to the stick) what is the measured length of the stick? 1. $L$ 2. $\gamma L$ 3. $L/\gamma$ 4. I'm sure it's B or C, but not sure which one 5. It depends Note: * Correct Answer: C
In particle decay the rate of decay is proportional to the number of particles left, $$\dfrac{dN}{dt} = -\lambda N$$ If we start with $N_0$ particles, what's the fraction of remaning particles in a time $\Delta t$? 1. $N_0 e^{-\lambda \Delta t}$ 2. $N_0 e^{+\lambda \Delta t}$ 3. $N_0 e^{-\Delta t/\lambda}$ 4. $N_0 e^{+\Delta t/\lambda}$ 5. Something else Note: * Correct answer: E * It's a fraction, so it's A without the number
In a particle detection experiment, the fraction of particles detected is: 1. underestimated 2. overestimated 3. the same as if we use the time of flight in the detector frame. Note: * Correct Answer: A
In our particle detection experiment, the fraction of particles detected at a given location in detector frame will be: $$e^{-\lambda \Delta t}$$ What is $\Delta t$ in this case? 1. The time to traverse from the source to the detector 2. The time observed on the clock on the wall 3. The time observed by the particles in their frame 4. None of these 5. More than one of these Note: * Correct answer: E? Definitely C, but could be A
Is the time interval ($\Delta t$) between two events Lorentz invariant? 1. Yes 2. No Note: * Correct answer: B
Is the proper time interval ($\Delta \tau = \dfrac{\Delta t}{\gamma}$) between two events Lorentz invariant? 1. Yes 2. No Note: * Correct answer: A