Which of the following is a true statement? a. electromagnetic waves consist of only changing electric fields. b. electromagnetic waves are longitudinal waves. c. electromagnetic waves do not always need a medium to travel. d. electromagnetic waves can vary in speed, wavelength and frequency.

What is the role of the ocular lens?

Explain the difference between each pair of concepts. a. frequency and relative frequency b. percentage and relative frequency a. select the correct choice below. a. frequency is the total number of observations in a data set. relative frequency is the number of times a particular distinct value occurs. b. frequency is the number of times a particular distinct value occurs. relative frequency is the ratio of the frequency of a value to the total number of observations. c. frequency is the total number of observations in a data set. relative frequency is the ratio of the number of times a particular distinct value occurs to the frequency. d. frequency is the number of times a particular distinct value occurs. relative frequency is the ratio of the frequency of two different values.

What is a good example of instantaneous speed