Appearance
❓:What is the magnitude of the emf induced in a conducting loop formed by a rod of length L = 10 cm moving at a constant speed v = 5 m/s along horizontal conducting rails, with the rod being a distance a = 10 mm from an infinitely long wire carrying a current I = 100 A?
🔑:To find the magnitude of the emf induced in the conducting loop, we first need to calculate the magnetic field at the location of the rod due to the current-carrying wire. The magnetic field (B) at a distance (a) from an infinitely long wire carrying a current (I) is given by the formula:[B = frac{mu_0 I}{2pi a}]where (mu_0) is the magnetic constant ((4pi times 10^{-7} , text{Tm/A})).Given:- (I = 100 , text{A})- (a = 10 , text{mm} = 0.01 , text{m})[B = frac{4pi times 10^{-7} , text{Tm/A} times 100 , text{A}}{2pi times 0.01 , text{m}}][B = frac{4pi times 10^{-5}}{2pi times 0.01}][B = frac{4 times 10^{-5}}{2 times 0.01}][B = frac{4 times 10^{-5}}{0.02}][B = 2 times 10^{-3} , text{T}]The emf (epsilon) induced in a conducting loop moving through a magnetic field is given by:[epsilon = B times v times L]where (v) is the speed of the loop and (L) is the length of the loop perpendicular to the magnetic field.Given:- (v = 5 , text{m/s})- (L = 10 , text{cm} = 0.1 , text{m})- (B = 2 times 10^{-3} , text{T})[epsilon = 2 times 10^{-3} , text{T} times 5 , text{m/s} times 0.1 , text{m}][epsilon = 1 times 10^{-3} , text{V}]So, the magnitude of the emf induced in the conducting loop is (1 times 10^{-3} , text{V}) or (1 , text{mV}).
❓:Suppose a physically realistic object of nontrivial size, such as a star, free-falls past a black hole. The center-of-mass trajectory for the object is hyperbolic and completely outside the black hole's photon sphere. The Roche limit for the object is inside the black hole's event horizon. What local forces cause the damage to the object, and how do they relate to the object's trajectory and the black hole's properties?
🔑:Tidal gravity is the local force that causes damage to the object, in the form of a stretching force along the direction of the gravity, and a squeezing force in the two directions orthogonal to the gravity. This is essentially the same force that causes the tides on Earth due to the Moon's gravity, although in the case of a black hole, the force is much stronger. The strength of the tidal gravity depends on the gradient of the gravitational field across the object, which in turn depends on the curvature of spacetime, i.e., on the Riemann curvature tensor (R_{alphabetagammadelta}). The Riemann tensor can be decomposed into its electric and magnetic parts, (E_{alphabeta}) and (B_{alphabeta}), with respect to an observer's 4-velocity (u^{alpha}):[E_{alphabeta}equiv R_{alphagammabetadelta}u^{gamma}u^{delta},qquad B _{alphabeta}equivfrac{1}{2}eta_{alphagammaepsilonzeta}R^{epsilon zeta}{}_{betadelta}u^{gamma}u^{delta}.] (10.52)The electric part (E_{alphabeta}) gives the tidal gravity, while the magnetic part (B_{alphabeta}) gives the gravitational force on moving objects due to the rotation of the source, known as "frame-dragging." For the case of a static black hole, the frame-dragging effect is zero. The strength of the tidal gravity can be estimated by considering the difference in the gravitational acceleration across the object. For a spherical object of radius (r_{0}) and center-of-mass at a distance (r) from the black hole of mass (M), the gravitational acceleration at the side of the object closest to the black hole is (sim GM/r^{2}), while the acceleration at the side farthest from the black hole is (sim GM/(r+2r_{0})^{2}). The difference in acceleration is[Delta gsimfrac{GM}{r^{2}}-frac{GM}{(r+2r_{0})^{2}}simfrac{4GM}{r^{3}}r_ {0},] (10.53)for (r_{0}ll r). This gives an estimate of the strength of the tidal gravity. The actual calculation of the tidal gravity requires a careful analysis of the geodesic deviation equation for the object's worldline, which can be quite complicated.
❓:Given a language L and two strings x and y, define x and y to be indistinguishable by L, denoted x equiv_L y, if for every string z, xz in L whenever yz in L. Prove that equiv_L is an equivalence relation, showing that it satisfies the properties of reflexivity, symmetry, and transitivity.
🔑:## Step 1: ReflexivityTo prove that equiv_L is reflexive, we need to show that for every string x, x equiv_L x. This means we must demonstrate that for any string z, xz in L whenever xz in L, which is trivially true since xz is the same in both cases.## Step 2: SymmetryFor symmetry, we need to prove that if x equiv_L y, then y equiv_L x. Given x equiv_L y, we know that for every string z, xz in L whenever yz in L. To show y equiv_L x, we consider any string z and observe that if yz in L, then because x equiv_L y, it must be that xz in L, satisfying the condition for y equiv_L x.## Step 3: TransitivityTo prove transitivity, we must show that if x equiv_L y and y equiv_L z, then x equiv_L z. Given x equiv_L y and y equiv_L z, we know that for any string w, if yw in L, then xw in L (from x equiv_L y), and if zw in L, then yw in L (from y equiv_L z). Thus, if zw in L, it implies yw in L, and consequently, xw in L, demonstrating x equiv_L z.The final answer is: boxed{equiv_L}
❓:What prevents bosons from occupying the same location in space, considering the principles of quantum mechanics and the nature of bosons in systems such as Bose-Einstein condensates?
🔑:In quantum mechanics, bosons are particles that follow Bose-Einstein statistics, which allows them to occupy the same quantum state, including the same location in space, without any restrictions. In fact, bosons are known to exhibit a phenomenon called "bose condensation," where a large number of bosons can occupy the same quantum state, including the same location, at very low temperatures. This is the basis for the formation of Bose-Einstein condensates (BECs).However, there are some subtleties to consider. While bosons can occupy the same quantum state, they are still subject to the Heisenberg uncertainty principle, which dictates that there is a fundamental limit to the precision with which certain properties, such as position and momentum, can be known simultaneously.In the context of BECs, the bosons are not exactly at the same location in space, but rather, they are described by a wave function that is delocalized over a region of space. This wave function, also known as the condensate wave function, is a solution to the Gross-Pitaevskii equation, which describes the behavior of a BEC.The condensate wave function is a many-body wave function that describes the collective behavior of the bosons, and it is peaked at a specific location in space, which is the center of the condensate. However, the wave function has a finite width, which reflects the uncertainty principle, and it is not exactly zero at any point in space.In other words, while the bosons in a BEC can occupy the same quantum state, they are not exactly at the same location in space, but rather, they are described by a delocalized wave function that reflects the uncertainty principle.It's worth noting that, in some cases, such as in the presence of strong interactions or in certain types of bosonic systems, the bosons may exhibit behavior that is similar to fermions, such as the formation of a "fermion-like" state, where the bosons appear to be excluded from occupying the same location in space. However, this is not a fundamental property of bosons, but rather a consequence of the specific interactions or conditions present in the system.In summary, bosons can occupy the same location in space, but the uncertainty principle and the delocalized nature of the condensate wave function ensure that they are not exactly at the same point in space. The behavior of bosons in BECs is a fascinating topic that continues to be an active area of research in condensed matter physics.