A breathalyzer is a portable electrochemical instrument that measures the concentration of ethyl alcohol in a sample of exhaled breath. A forensic chemist checks the calibration of a breathalyzer by testing a standard air sample known to contain 0.174 mg/L of ethanol seven times. The average value of these seven replicate measurements is found to be 0.162 mg/L . Calculate the absolute error of the breathalyzer.

The frequency of vibrations of a vibrating violin string is given by f = 1 2l t ρ where l is the length of the string, t is its tension, and ρ is its linear density.† (a) find the rate of change of the frequency with respect to the following. (i) the length (when t and ρ are constant) (ii) the tension (when l and ρ are constant) (iii) the linear density (when l and t are constant) (b) the pitch of a note (how high or low the note sounds) is determined by the frequency f. (the higher the frequency, the higher the pitch.) use the signs of the derivatives in part (a) to determine what happens to the pitch of a note for the following. (i) when the effective length of a string is decreased by placing a finger on the string so a shorter portion of the string vibrates df dl 0 and l is ⇒ f is ⇒ (ii) when the tension is increased by turning a tuning peg df dt 0 and t is ⇒ f is ⇒ (iii) when the linear density is increased by switching to another string df dρ 0 and ρ is ⇒ f is ⇒

Sodium chloride, nacl, is formed when a sodium atom transfers its electron to a chlorine atom. the difference in charge between the two atoms creates a(n) attraction that bonds them together.

The direction of the current in an alternating current circuit remains constant. is direct. changes repeatedly. changes randomly.