The current in a 100 watt lightbulb is 0.80 A. The filament inside the bulb is 0.30 mm in diameter. a) What is the current density of the filament? b) What is the electron current in the filament, in electrons per second?

A microwave beam with a wavelength of 1.5 cm has an intensity of 13 W/m2. What is the magnetic field amplitude? (

Field of a circular loop: Two coaxial circular coils of radius R = 15 cm, each carrying 4.0 A in the same direction, are positioned a distance d = 20 cm apart, as shown in the figure. Calculate the magnitude of the magnetic field halfway between the coils along the line connecting their centers. (μ0 = 4π × 10-7 T ∙ m/A)

The current through inductance L is given by 

In proton-beam therapy, a high-energy beam of protons is fired at a tumor.  As  the protons stop in the tumor, their kinetic energy breaks apart the tumor’s DNA, thus killing the tumor cells. For one patient, it is desired to deposit 0.11 J of proton energy in the tumor. To create the proton beam, protons are accelerated from rest through a 1.2×104 kV potential difference. What is the total charge of the protons that must be fired at the tumor? 

What potential difference is needed to accelerate a He+ ion (charge +e, mass 4 u) from rest to a speed of 3.5 x 106 m/s? (mass of a proton = 1.67 x 10-27 kg, charge of electron = 1.6 x 10-19 C)

a) How long must a 0.54 mm diameter aluminum wire be to have a 0.56 A current when connected to the terminals of a 1.5 V flashlight battery? (Resistivity of aluminum = 2.8 x 10-8

In proton-beam therapy, a high-energy beam of protons is fired at a tumor.  As  the protons stop in the tumor, their kinetic energy breaks apart the tumor’s DNA, thus killing the tumor cells. For one patient, it is desired to deposit 0.08 J of proton energy in the tumor. To create the proton beam, protons are accelerated from rest through a 8.0×103 kV potential difference. What is the total charge of the protons that must be fired at the tumor? 

What potential difference is needed to accelerate a He+ ion (charge +e, mass 4 u) from rest to a speed of 7.0 x 105 m/s? (mass of a proton = 1.67 x 10-27 kg, charge of electron = 1.6 x 10-19 C)

a) How long must a 0.64 mm diameter aluminum wire be to have a 0.60 A current when connected to the terminals of a 1.5 V flashlight battery? (Resistivity of aluminum = 2.8 x 10-8