The dipole moment of water is p = 6.17 x 10-30 C m. If the electric field in a microwave oven is on average 94.7 x 10-6 N/C, and water molecules start anti-parallel to the external field (180o), how much energy (in Joules) is deposited into a water sample in 2.39 seconds with 13.1 of water if the direction of this field switches every 3.42 x 108 times a second and each time the electric field flips the water molecules align themselves with the new direction?

Explanation:

Given that:

p = 6.17 × 10⁻³⁰ Cm

Electric field E = 94.7 × 10⁻⁶ N/C

Then:

∴

This implies that one switch of dipole produces 2pE energy to be deposited in the water.

mass of water = 13.1 g

The number of water molecule =

=

= 4.38 × 10²³ molecules of water.

∴ Number of dipoles = 4.38 × 10²³

The total number of switches in 2.39  sec = switch frequency × 2.73

Number of switches = 2.39 × 3.42 × 10⁸

Number of switches = 817380000

Number of switches = 8.174  × 10⁸

The total energy Q deposited = Energy deposited per dipole × Number of dipole × no of switches

Q = (2pE) × 4.38 × 10²³ × 8.174  × 10⁸

Q = (2 × 6.17 × 10⁻³⁰ × 94.7 × 10⁻⁶  × 4.38 × 10²³ × 8.174  × 10⁸ )

Q = 0.41838 J

powerful computers now, not then

the duration of a photographic flash is related to an rc time constant, which is 0.100 μs for a certain camera.