Physics Test 2

F=IBlsin(t)

(a) A 0.750-m-long section of cable carrying current to a car starter motor makes an angle of 60º with the Earth's 5.50×10−5 T field. What is the current when the wire experiences a force of 7.00×10−3 N ? (b) If you run the wire between the poles of a strong horseshoe magnet, subjecting 5.00 cm of it to a 1.75-T field, what force is exerted on this segment of wire?

Induced emf: e=Blv The magnitude is too small to really affect the jets' path

17. (a) A jet airplane with a 75.0 m wingspan is flying at 280 m/s. What emf is induced between wing tips if the vertical component of the Earth's field is 3.00×10−5 T ? (b) Is an emf of this magnitude likely to have any consequences? Explain.

Mutual Inductance: emf(2)= -M* d(I)/d(t) emf(2): induced emf in the second coil -M is the mutual inductance d(i) is the change in current of first coil

55. Two coils are placed close together in a physics lab to demonstrate Faraday's law of induction. A current of 5.00 A in one is switched off in 1.00 ms, inducing a 9.00 V emf in the other. What is their mutual inductance?

Inductive Reactance: X(l)=2(pi)fl X(l) is the inductive reactance, l is the frequency and L is inductance

At what frequency will a 30.0 mH inductor have a reactance of 100 Ω?

Induced magnetic field e=Blv

18. (a) A nonferrous screwdriver is being used in a 2.00 T magnetic field. What maximum emf can be induced along its 12.0 cm length when it moves at 6.00 m/s? (b) Is it likely that this emf will have any consequences or even be noticed?

First find Area of Coil: A=(pi)/4 * d^2 Then use Equation to find angular velocity: E(0)=NAB{*} where {*} is the angular momentum

29. At what angular velocity in rpm will the peak voltage of a generator be 480 V, if its 500-turn, 8.00 cm diameter coil rotates in a 0.250 T field?

Calculate voltage output from relation: V(s)/V(p)= N(s)/N(p) Calculate input current from relation: I(p)/I(s)=N(s)/N(p) Calculate input power: P(in)=I(p)*V(p)

47. (a) What is the voltage output of a transformer used for rechargeable flashlight batteries, if its primary has 500 turns, its secondary 4 turns, and the input voltage is 120 V? (b) What input current is required to produce a 4.00 A output? (c) What is the power input?

First find Current: I=P/V where P is power and V is voltage Unit: W/V = Ampere Then find Magnetic field strengths (long,straight,wire): B=(Unaught)i/2(pi)r

72. Calculate the size of the magnetic field 20 m below a high voltage power line. The line carries 450 MW at a voltage of 300,000 V.

Time constant of RL circuit: t= L/R Then find initial current: I(0)= V/R Then find growth of current: I=I(0) * e^(-t/Time constant)

74. (a) What is the characteristic time constant of a 25.0 mH inductor that has a resistance of 4.00 Ω? (b) If it is connected to a 12.0 V battery, what is the current after 12.5 ms?

Self Inductance: emf= -L * d(i)/d(t)

8. A device is turned on and 3.00 A flows through it 0.100 ms later. What is the self-inductance of the device if an induced 150 V emf opposes this?

Induced emf: e=N(d(Mag. flux)/d(t)) Magnetic flux: d(Mag. flux)=d(BA) Magnetic flux, and induced emf can be used to find induced (e): e=Nd(BA)/d(t) ; if B is uniform; $$$$$$e=NB(d(A)/d(t)) where d(A)=A(f)-A(i) and A(i)=0 Magnetic flux is decreasing, so the direction of the current will be to aid the decreasing flux $decrease= CLOCKWISE

8. Suppose a 50-turn coil lies in the plane of the page in a uniform magnetic field that is directed into the page. The coil originally has an area of 0.250 m2 . It is stretched to have no area in 0.100 s. What is the direction and magnitude of the induced emf if the uniform magnetic field has a strength of 1.50 T?

First find Resistance: I=V/R Then find net current: I=V(s)-V(b)/R V(b) is back emf

9. Suppose a motor connected to a 120 V source draws 10.0 A when it first starts. (a) What is its resistance? (b) What current does it draw at its normal operating speed when it develops a 100 V back emf?

r=mv/qB

A proton moves at 7.50×107 m/s perpendicular to a magnetic field. The field causes the proton to travel in a circular path of radius 0.800 m. What is the field strength?

F=qvBsin(t)

An electron moving at 4.00×103 m/s in a 1.25-T magnetic field experiences a magnetic force of 1.40×10−16 N . What angle does the velocity of the electron make with the magnetic field? There are two answers

t=NIABsin(t) A=area on each turn Area of square loop A=x^2 x is the length of side

Find the current through a loop needed to create a maximum torque of 9.00 N ⋅ m. The loop has 50 square turns that are 15.0 cm on a side and is in a uniform 0.800-T magnetic field.

Magnetic field strength at center of loop B=(Unot)NI/2R Where R is the radius of the loop

Inside a motor, 30.0 A passes through a 250-turn circular loop that is 10.0 cm in radius. What is the magnetic field strength created at its center?

(F/l)=(U{0 i1 i2)/2(pi)r

The wire carrying 400 A to the motor of a commuter train feels an attractive force of 4.00×10−3 N/m due to a parallel wire carrying 5.00 A to a headlight. (a) How far apart are the wires? (b) Are the currents in the same direction?

Capacitive Reactance: X(c)= 1/2(pi)fC

What capacitance should be used to produce a 2.00 MΩ reactance at 60.0 Hz?