A step-down transformer is to be used to convert an ac voltage of $120 \mathrm{~V}$ to $6 \mathrm{~V}$ to power an electric train. If there are 300 turns in the primary coil, how many turns should there be in the secondary coil?

Two current-carrying wires are parallel to one another and separated by $1 \text{ cm}$. If the distance between them is increased to $2 \text{ cm}$ the new force will be what factor times the original force?

Two current-carrying wires are parallel to one another and have a separation of 25 cm. If the wires carry opposite currents of 11 A each, what is the magnitude of the total magnetic field midway between them?

A wire coil with 120 turns and a cross-sectional area of $0.03 \mathrm{~m}^2$ is perpendicular to a magnetic field of magnitude $1.8 \mathrm{~T}$. In $0.4 \mathrm{~s}$, the coil is rapidly removed from the magnetic field. a. What is the coil's initial magnetic flux? b. What is the average value of the induced voltage in the coil?

When a rubber rod is rubbed with rabbit fur, the rod becomes a) negatively charged. b) positively charged. c) neutral. d) either negatively charged or positively charged, depending on whether the fur is always moved in the same direction or is moved back and forth.

Which of the following is true about the voltage in a series circuit?
The total of all voltage drops must:
$a)$ equals the total current.
$b)$ adds up to zero.
$c)$ adds up to the total voltage supplied by the battery.
$d)$ never exceeds the total circuit resistance.

The objective lens of a telescope has a focal length of 1.0 m. An object is located at a distance of 10 m from the lens.

At what distance from the objective lens is the image fored by this lens?

A magnifying glass with a focal length of $+4 \mathrm{~cm}$ is placed $2 \mathrm{~cm}$ above a page of print.

What is the magnification of this image?

A negative lens has a focal length of -10 cm. An object is located 20 cm from the lens.

How far from the lens is the image?

Suppose a fixed distance separates the centers of two circular loops. What relative orientation of the loops will give the maximum mutual inductance? What orientation will give the minimum mutual inductance?

If we look down at the top of a circular loop of wire whose plane is horizontal and that carries a current in the clockwise direction, what is the direction of the magnetic field at the center of the circle? Explain.

Test your vocabulary by matching each term to its definition, as identified by its preceding letter code. A. The number of Individuals of a species per unit area or volume. B. The functional role of an organism in its environment, including its activities and interactions with other organisms. C. The maximum number of a species that can be supported indefinitely by the environment. D. Exploitation in which one organism kills and eats another, usually of a different species. E. A term for any non-living part of the environment, e.g. rainfall, temperature. F. The area where an animal normally lives and moves about in. G. Any living component of the environment (or aspect of it) that has an effect on another organism in the environment. H. Community of interacting organisms and the environment (both biotic and abiotic) in which they both live and interact. I. An interaction between two species where both species benefit. J. Competition for a resource between members of the same species. K. The physical place or environment where an organism lives. It includes all the physical and biotic factors. L. Competition for a resource between members of different species. M. All the individuals of a particular species within a set area. N. An interaction between organisms exploiting the same resource. a. abiotic factor b. biotic factor c. carrying capacity d. competition e. density f. ecosystem g. habitat h. home range i. interspecific competition j. intraspecific competition k. mutualism l. niche m. population n. predation

A generator coil has 25 turns of wire and a cross-sectional area of 36 $\mathrm{c m}^{2}$. The maximum emf developed in the generator is 2.8 V at 60 Hz. What is the strength of the magnetic field in which the coil rotates?

A loop with 37 turns and an area of 0.33 m2 is rotating at 281 rad/s. The loop's axis of rotation is perpendicular to a uniform magnetic field with a strength of 0.035 T. What is the maximum emf induced? (Hint: Use the expression maximum $\mathrm{emf}=N A B \omega$.)