Astudent is measuring the effects of an electric circuit on a compass, and he is testing to see increasing the current will cause the compass needle to change direction faster. he does one trial using a 9-volt battery and another trial using a 1.5 volt battery. he takes accurate data. based on good experimental design, which would improve his experiment? a. he should use batteries of the same voltage but from different manufacturers to show he has used different variables. b. he should add a nonworking compass to act as a control. c. he should repeat the test with three additional batteries of varying voltages to demonstrate the reproducibility of results. d. he should use only one battery but do several trials using different circuit designs to ensure he is appropriate test groups. ( i think it's a or c)

Lin yao looks at the back of a spoon. how should she describe her reflection? upside down and smaller upside down and larger right-side up and smaller right-side up and larger

Chapter 23, problem 075 the figure shows a geiger counter, a device used to detect ionizing radiation (radiation that causes ionization of atoms). the counter consists of a thin, positively charged central wire surrounded by a concentric, circular, conducting cylindrical shell with an equal negative charge. thus, a strong radial electric field is set up inside the shell. the shell contains a low-pressure inert gas. a particle of radiation entering the device through the shell wall ionizes a few of the gas atoms. the resulting free electrons (e) are drawn to the positive wire. however, the electric field is so intense that, between collisions with gas atoms, the free electrons gain energy sufficient to ionize these atoms also. more free electrons are thereby created, and the process is repeated until the electrons reach the wire. the resulting "avalanche" of electrons is collected by the wire, generating a signal that is used to record the passage of the original particle of radiation. suppose the radius of the central wire is 24 âµm, the inner radius of the shell 2.3 cm, and the length of the shell 14 cm. if the electric field at the shell's inner wall is 2.8 ă— 104 n/c, what is the total positive charge on the central wire?

When the displacement of a mass on a spring is 12a the half of the amplitude, what fraction of the mechanical energy is kinetic energy? at what displacement, as a fraction of a, is the mechanical energy half kinetic and half potential?