Q: A coil is placed in a uniform magnetic field and connected to a battery of 6.00 V with a resistance of 3.00 Ω. The coil has 50 turns and a side length of 0.0860 m. What is the initial torque on the coil?

$$2.74 \times 10$$^{-3}$$\ \mathrm{N\ m}$$

Q: A photon has an energy of $$1.81\ \mathrm{keV}. $$What is its wavelength?

$$6.87 \times 10$$^{-10}$$\ \mathrm{m}$$

Q: A galaxy is receding at $$4.5\% of $$the speed of light. Using $$1\ \mathrm{Mpc} = 3.09 \times 10$$^{19}$$\ \mathrm{km}$$, estimate its distance in km.

$$6.8 \times 10$$^{20}$$\ \mathrm{km}$$

Q: What is the de Broglie wavelength of a $$0.60\ \mathrm{kg}$$ basketball moving at $$10.0\ \mathrm{m\ s$$^{-1}$$}$$?

$$1.1 \times 10$$^{-34}$$\ \mathrm{m}$$

Question 1

A coil is placed in a uniform magnetic field and connected to a battery of 6.00 V with a resistance of 3.00 Ω. The coil has 50 turns and a side length of 0.0860 m. What is the initial torque on the coil?

Accepted Answer

$$2.74 	imes 10$$^{-3}$$\ \mathrm{N\ m}$$

Question 2

A car travels around a banked curve of fixed radius. If the angle $$	heta of $$the bank is increased while the mass and radius remain constant, what happens to the maximum speed at which the car can travel without skidding?

Accepted Answer

It increases because $$F_c = \frac{mv^2$}{r}$$ and $$F_c$$ increases with $$	heta.$$

Question 3

A photon has an energy of $$1.81\ \mathrm{keV}. $$What is its wavelength?

Accepted Answer

$$6.87 	imes 10$$^{-10}$$\ \mathrm{m}$$

Question 4

A ball is thrown horizontally from a castle wall 51.0 m high with an initial velocity of $$45.8\ \mathrm{m\ s$$^{-1}$$} at$$ $$50.0^\circ$$ above the horizontal. How far above the wall does the ball pass?

Accepted Answer

$$4.06\ \mathrm{m}$$

Question 5

Which statement best describes how electrons are liberated from a metal target by incoming photons in the photoelectric effect?

Accepted Answer

Electrons are released if the photon energy exceeds the work function of the metal.

Question 6

According to Lenz’s law, what is the direction of the induced current when a north pole magnet approaches a solenoid?

Accepted Answer

The current flows to create a north pole at the approaching end, opposing the change.

Question 7

A galaxy is receding at $$4.5\% of $$the speed of light. Using $$1\ \mathrm{Mpc} = 3.09 	imes 10$$^{19}$$\ \mathrm{km}$$, estimate its distance in km.

Accepted Answer

$$6.8 	imes 10$$^{20}$$\ \mathrm{km}$$

Question 8

What is the de Broglie wavelength of a $$0.60\ \mathrm{kg}$$ basketball moving at $$10.0\ \mathrm{m\ s$$^{-1}$$}$$?

Accepted Answer

$$1.1 	imes 10$$^{-34}$$\ \mathrm{m}$$

Question 9

Which of the following particles is NOT bound by the strong nuclear force?

Accepted Answer

Neutrino

Question 10

A metal bar of length $$\ell$$ moves at constant velocity $$v$$ through a magnetic field $$B$$, with resistance $$R$$ and mass $$m. $$What is the expression for $$v in $$terms of $$m, g, R, B, \ell$$?

Accepted Answer

$$v = \frac{mgR}{B^2$ \$$ell^2$$}$$

Question 11

A charged particle moves near a long straight wire carrying current $$I. At a $$distance $$r$$ from the wire, what is the magnetic field strength?

Accepted Answer

$$B = \frac{\mu_0$ I}{2\pi r}$$

Question 12

Why does a charged particle not move in a perfect circle near a current-carrying wire?

Accepted Answer

Because $$B$$ decreases with $$r$$, so the magnetic force is not constant.

Question 13

Two parallel wires carry equal currents in opposite directions. At the midpoint between them, a charge $$q is $$placed. What is the net force on $$q$$?

Accepted Answer

Zero, because the magnetic fields cancel at the midpoint.

Question 14

A spaceship A moves at $$0.700c$$ relative to S, and B moves at $$-0.700c$$ relative to S. What is the velocity of A as measured by B?

Accepted Answer

$$0.940c$$

Question 15

A moon orbits a planet with period $$T. $$Using Kepler’s third law, what is the relationship between orbital speed $$v$$ and orbital radius $$r$$?

Accepted Answer

$$v = \sqrt{\frac{GM}{r}}$$

Question 16

A steel wire under tension $$T$$ vibrates with frequency $$f$$ and length $$L. $$What is the correct formula relating $$T$$, $$f$$, $$L$$, and mass per unit length $$\mu$$?

Accepted Answer

$$T = 4\mu L^2$ f^2$

Question 17

A proton enters a uniform electric field between two plates. If the force on the proton is $$1.92 	imes 10$$^{-14}$$\ \mathrm{N}$$ downward, what is the acceleration of the proton? ($$m_p = 1.67 	imes 10$$^{-27}$$\ \mathrm{kg})$$

Accepted Answer

$$1.15 	imes 10$$^{13}$$\ \mathrm{m\ s$$^{-2}$$}$$

Question 18

Unpolarised light passes through a polarising filter. According to Malus’ Law, what is the intensity of the transmitted light if the filter’s axis is at $$60^\circ to $$the incident polarisation?

Accepted Answer

$$I = I_0$ \cos^2$ 60^\circ = 0.25 I_0$

Question 19

When light passes through a polarising filter, why does the transmitted energy decrease?

Accepted Answer

Fewer photons are transmitted per second; the energy per photon remains unchanged.

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