Integrated Concepts Police radar determines the speed of motor vehicles using the same Doppler-shift technique employed for ultrasound in medical diagnostics. Beats are produced by mixing the double Doppler-shifted echo with the original frequency. If 1.50109 -Hz microwaves are used and a beat frequency of 150 Hz is produced, what is the speed of the vehicle? (Assume the same Doppler-shift formulas are valid with the speed of sound replaced by the speed of light.)

Lecture 2 1 iClicker question Y ou place same two charges a distance r apart. Then you double each charge and double the distance between the charges. How does the force between the two charges change a) The new force is twice a large. b) The new force is half as large. c) The new force is four times as large. d) The new force is four times smaller. e) The new force is the same 2 Electric Force - Coulomb’s Law Consider two electric charge1: q and q 2 The electric force F between these two charges separated by a distance r is given by Coulomb’s Law The constant k is called Coulomb’s constant and is given by Coulomb’s law in vector form q 1 2 12 F = k r 2 r 12 12 32 q1 2 q2 (2q) 2 q2 F = k = k → k = k r 2 r2 (2r) 2 r2 Force remains the same 4 Demo: electrostatic charging 5 +++ ---