You leave a thick metal spoon with no sharp edges in your ceramic coffee mug as you reheat the coffee in the microwave oven. While the microwave oven is operating,

A key difference between laser light and sunlight is that laser light

During a head-on collision between cars, the front ends of those cars crumple strategically. Why is it helpful to have the front end of a car—the portion under the car's hood—crush to a shorter length during a head-on collision?

A nuclear fission chain reaction is sustained by neutrons: neutrons from one shattered nucleus induce fissions in other fissionable nuclei. Those fissions also release protons, but protons don't induce fissions because

As you talk on your cellphone, an electric current flows from the positive terminal of the phone's battery, through a metal wire, to the positive terminal of the phone's electronics. Compare the voltage at the battery's positive terminal to the voltage at the electronics' positive terminal.

You are purchasing LED bulbs for your apartment and you have a choice of 5000K (5000 kelvin) bulbs that imitate sunlight and 2700K (2700 kelvin) bulbs that imitate old-fashioned incandescent (tungsten) bulbs. Compared those in a 2700K bulb, the LEDs in a 5000K bulb

If you hold your camera too close to your subject, the camera will be unable to take a sharp photograph of that subject. Why can't the camera focus on objects that are too close to its lens?

After a narrow laser beam passes through a converging lens, its diameter decreases to

On a clear day, the sky appears blue because some visible light from the sun experiences Rayleigh scattering. Sunlight also contains infrared and ultraviolet light. Do they experience significant Rayleigh scattering?

You are watching children play at the local swimming pool. Two children jump off the side of the pool at the same time. They both jump equally hard, but the girl jumps mostly upward while the boy jumps mostly forward. After they leave the side of the pool,

A gymnast doing a double backflip leaps off the floor with her arms and legs extended and then pulls herself into a very compact position. In her compact shape, she rotates very rapidly and completes two full rotations before opening back up to land on the floor. During the time that she is not touching the floor, the one aspect of her motion that is constant is

Early telegraph messages were sent using Morse code, simple patterns of long and short clicks that represented letters and numbers. For example, the three letters "SOS" are represented by short-short-short (pause) long-long-long (pause) short-short-short. What category of representation is Morse code using?

An argon atom has 18 electrons. When an argon atom is in its ground state, how many different standing waves (orbitals) are occupied (used) by that atom's electrons?

You use a converging lens to project the image of a flower on the wall of your dorm room. What should that lens do to form a sharp image of the flower on the wall?

Suppose both coils of an ordinary transformer are carrying constant electric currents. Why can't the transformer transfer electric power from one coil to the other?

You and your friends are riding skateboards down a hill. There are two paths from the top of the hill to the bottom: both are smooth ramps, but the steeper one is exactly half as long as the shallower one. You take the shorter, steeper ramp and your friend takes the longer, shallower ramp. Neglecting friction and air resistance,

When you look into an aquarium from the front, its sides appear to be perfect mirrors. Even though the sides are ordinary glass, they offer perfect reflections of the fish. This effect, where light bounces from the outer layer of glass when it tries to get out of the glass at a shallow angle is an example of total internal reflection, which occurs when

A magnifying glass is a converging lens that can form real images, just like a camera lens. You hold a magnifying glass 5 inches from the wall of your room and it forms a sharp image on the wall of the window at the other side of the room. There is a tree outside the window. To form a sharp image of the tree on the wall, you must move the magnifying glass

When you reduce the aperture (effective diameter) of the lens in your camera,

If you remove a strong permanent magnet suddenly from within a metal ring, an electric field will appear in the metal ring and an electric current will flow through that ring. If you remove the same magnet suddenly from within a glass ring,

The light emitted by the low-density neon gas in a neon sign appears red and medium bright. If the sign contained high-density neon gas, the light it emitted would appear

Sunlight reflected from a soap bubble appears brightly colored because

Laser pointers come in a variety of colors, including green, red, and violet. Why are there no white laser pointers?

A microwave oven moves the food around on a carousel to obtain relatively even heating. Motionless food would heat unevenly because

The glass tube of a fluorescent lamp contains mercury vapor. An electric discharge in that low-density vapor produces light. How does the white powder on the inside of the glass tube affect the light emitted by the fluorescent lamp?

A battery charger recharges a battery by

A twist-tie is a long, thin, sharp metal wire wrapped in paper. If you place a twist-tie in a microwave oven and turn the oven on, what will happen to the twist-tie?

You are arm-wrestling a friend. While you are gradually winning the competition, compare the torque that your arm exerts on your friend's arm to the torque your friend's arm exerts on your arm.

An electrical insulator cannot conduct electric current because

If the speed of light in water did not depend on the wavelength of that light, a rainbow would

You are pulling a toy wagon up a steep hill and the wagon is traveling in a straight line at a steady pace. The net force that the wagon is experiencing

The transformer in advertising sign has 120 turns in its primary coil and 480 turns in its secondary coil. With 120-volt AC power connected to the primary coil and a current of 1 ampere flowing through that primary coil, the transformer's secondary coil is supplying

The MOSFET device that we discussed in class is formed by placing a piece of p-type semiconductor between two pieces of n-type semiconductor. When there is zero charge on this MOSFET's gate surface, its middle portion (the "channel") cannot conduct electric current because

An LED (a light-emitting diode) emits light when an electron that has crossed the pn-junction from the

In the United States, the licensed radio wave frequencies of two different AM radio stations in the same city are always separated by at least 10,000 cycles per second (10 kilohertz). Why can't two stations use radio wave frequencies separated by only 1 cycle per second (1 hertz)?

Near high voltage power lines, there are

The constituents of a radioactive nucleus are in stable equilibrium, yet they eventually rearrange spontaneously in a way that allows the nucleus to fall apart and release stored energy. What allows the nucleus to escape from its stable equilibrium and subsequently fall apart?

Like the back of a credit card, your ID card has a magnetic strip on it. The pattern of magnetization on that strip represents information about you. The magnetic strip is made from a material that is

A person who is "nearsighted" sees nearby objects clearly but can't focus on a distant landscape. That landscape appears blurry because each eye forms its real image in front of the retina. To move the real image of the landscape away from the lens so that its image forms on the retina, the person should wear glasses that contain

A DVD player uses a red diode laser to read the disk, whereas a Blue-ray player uses a blue diode laser to read the disk. Switching from a red laser to a blue laser allows the Blu-ray disk to hold far more information than a DVD. What is it about blue light that allows for the increase in data storage?

When p-type semiconductor and n-type semiconductor touch, they form a pn-junction. A few electrons spontaneously migrate from conduction levels in the n-type side to valence levels in the p-type side. The pn-junction therefore develops

During a particular brown out, the voltage of the electrical power provided to your home by the power company is reduced by 5%. The voltage drop across your reading lamp is reduced by 5% so the current passing through it is also reduced by 5%. Overall, the power consumed by the lamp

An electrically charged ball emits an electromagnetic wave that travels across the universe when it is

Running on soft dry sand is exhausting, so you switch to running on hard wet sand. The hard wet sand takes less energy from you because

Separating uranium-235 atoms from uranium-238 atoms is extremely difficult because both atoms have the same number of

When an electric charge moves through a steady magnetic field, the electric charge

The current passing through a metal wire is proportional to

Two LEDs (light emitting diodes) are identical except that the conduction and valence levels of the LED #1 are separated by more energy than those of LED #2. Because of that difference, LED #1 emits

At this moment in time, a water bottle is touching only one thing: the top of a table. The downward force the water bottle is exerting on the table right now

A large sugar crystal is almost perfectly clear. If you crush that crystal, it becomes white because

You have two identical electric space heaters, both of which are plugged into the same electrical outlet of your home. It's a cold winter day and you turn on one of the heaters. A current of 8 amperes flows through the wires of your home (to provide power to the heater) and wastes 1 watt in those wires. When you turn on the second heater, a current of

Car windshields are made from safety glass, a tough 3-layer sandwich of glass, plastic, and glass. The plastic's index of refraction is almost identical to the glass's index of refraction. What would happen if those indices of refraction were significantly different from one another?

Atoms are often drawn as having planet-like electrons traveling in circular orbits around a sun-like nucleus. This characterization is naive primarily because the electrons in an atom

When a microwave is heating food in a microwave oven, the aspect of that microwave that is primarily responsible for heating the food is its

Your beach towel has parts dyed fluorescent orange and parts dyed fluorescent blue. When exposed to pure ultraviolet let, those parts glow orange and blue respectively. Go Hoos! When exposed to pure green light, the orange parts glow orange but the blue parts appear dark because

You are listening to an AM radio station while sailing your sailboat in the Atlantic Ocean. You can see the station's vertical transmitting antenna 10 miles to your west. As that station's radio wave passes by you, its electric field points

When light that had been traveling through empty space enters a gas, the light slows down slightly. What characteristic of the gas is responsible for slowing the light?

The electric power grid in the United States uses alternating current because

A tank circuit consists of two simple components, a capacitor and an inductor. Tank circuits are useful in radio and many other electrical and electronic systems because they are

A 120-volt AC electrical outlet in the United States has two slots, known as neutral and power (or hot). Which slot sometimes has a voltage of +130 volts and which slot sometimes has a voltage of –130 volts?