PHY 2049 Flashcards (Q&A Style)
Use these flashcards to quiz yourself. Cover the answer section and try to recall the solution from
memory. All content is derived from Young & Freedman (15th Edition).
Flashcard Questions
Q1: Electric Field of a Ring of Charge
A ring of radius 10.0 cm carries a total charge of +4.00 C uniformly distributed. What is the electric
field at a point on the axis 20.0 cm from the center?
Q2: Electric Potential of Point Charges
Two charges +2.00 C and -3.00 C are placed 1.00 m apart. Find the electric potential at the midpoint
between them.
Q3: Capacitance with Dielectric
A parallel-plate capacitor has area 0.01 m and plate separation 1 mm. A dielectric with = 3 is
inserted. What is the new capacitance?
Q4: Resistivity and Temperature
A copper wire has resistance 10.0 at 20C. What is its resistance at 80C? ( = 0.0039 /C)
Q5: Kirchhoff's Rules
In a loop with two resistors (4.00 and 6.00 ) and a 12.0 V battery, find the current through each
resistor using Kirchhoff's laws.
Q6: Field Inside Solenoid
A solenoid is 40.0 cm long and has 1000 turns. Find the magnetic field inside when it carries 3.00 A.
Q7: Force on Current-Carrying Wire
A 10.0 cm wire carries 5.00 A perpendicular to a 0.600 T magnetic field. Find the force on the wire.
Q8: Induced EMF in a Loop
A circular loop of radius 5.00 cm is in a magnetic field that increases at 0.020 T/s. What is the
induced emf?
Q9: Energy Stored in Inductor
An inductor of 0.500 H carries a current of 2.00 A. Find the energy stored in its magnetic field.
Q10: Wave Speed in Dielectric
Light travels in a medium with = 2.25 and = . What is the speed of light in this medium?
Q11: Poynting Vector Magnitude
An EM wave has peak E-field of 100 V/m. What is the average energy flux (S_avg)?
Q12: Refraction Snell's Law
Light passes from air into water (n = 1.33) at 30.0. What is the angle of refraction?
Q13: Image by Convex Lens
An object is 30.0 cm from a convex lens of f = 10.0 cm. Find the image distance and magnification.
Q14: Interference Pattern
In a double-slit experiment, d = 0.500 mm, L = 2.00 m, and = 600 nm. Find fringe spacing.
Q15: Single-Slit Diffraction Minimum
Light of 500 nm passes through a slit of width 0.050 mm. Find angle to first minimum.
Q16: Mirror Equation
A concave mirror has radius 40.0 cm. An object is 60.0 cm in front of it. Find image distance.
Q17: Thin Film Destructive Interference
A film (n=1.40) on glass (n=1.50) reflects 560 nm light destructively. What is the minimum
thickness?
Q18: Ray Diagrams
Describe how you would draw a ray diagram for an object outside the focal length of a converging
lens.
Flashcard Answers
A1: Electric Field of a Ring of Charge
1. Use the axial electric field formula for a ring: E = (1/4)(qz)/(z + R)^(3/2)
2. Plug in: z = 0.200 m, R = 0.100 m, q = 4.0010^-6 C
3. Solve and round to 3 significant figures.
A2: Electric Potential of Point Charges
1. V_total = V1 + V2 = (1/4)(q1/r1 + q2/r2)
2. r1 = r2 = 0.5 m; plug in values and solve
3. Pay attention to sign of charges
A3: Capacitance with Dielectric
1. Use C = A/d
2. Plug in values: = 3, = 8.8510^-12 F/m
3. Round to 3 sig figs
A4: Resistivity and Temperature
1. Use R = R[1 + (T - T)]
2. Plug in values and solve for R
3. Final answer in ohms, 3 sig figs
A5: Kirchhoff's Rules
1. Apply loop rule: V = IR1 + IR2
2. 12 = I(4 + 6) I = 1.20 A
3. Both resistors have same current in series
A6: Field Inside Solenoid
1. Use B = nI, where n = N/L
2. = 410^-7 Tm/A
3. n = 1000/0.4 = 2500 turns/m
4. Plug and solve
A7: Force on Current-Carrying Wire
1. Use F = ILB sin, = 90 sin = 1
2. L = 0.10 m, I = 5.00 A, B = 0.600 T
3. F = 0.300 N
A8: Induced EMF in a Loop
1. Use = d/dt = r * dB/dt
2. r = 0.05 m; plug and solve
A9: Energy Stored in Inductor
1. Use U = 0.5 * L * I
2. Plug in L = 0.500 H, I = 2.00 A
3. Final energy in joules
A10: Wave Speed in Dielectric
1. Use v = 1/sqrt()
2. Substitute values and solve
A11: Poynting Vector Magnitude
1. S_avg = (E_max)/(2c)
2. Plug in: E_max = 100 V/m, = 410^-7, c = 310^8
3. Final units: W/m
A12: Refraction Snell's Law
1. Use Snell's Law: nsin = nsin
2. Solve for
A13: Image by Convex Lens
1. Use 1/f = 1/do + 1/di
2. Then m = -di/do
A14: Interference Pattern
1. Use y = mL/d for m = 1
2. Solve for y
A15: Single-Slit Diffraction Minimum
1. Use a*sin = m with m = 1
2. Solve for
A16: Mirror Equation
1. f = R/2 = 20.0 cm
2. Use 1/f = 1/do + 1/di
A17: Thin Film Destructive Interference
1. Use 2nt = (m + 0.5) for m = 0
2. Solve: t = / (4n)
A18: Ray Diagrams
1. Draw three rays: parallel (refracts through focus), through center (straight), through focus (exits
parallel)
2. Locate image where rays converge