Latest Physical Science Reviewer 7

1. Which statement about the North-magnetic pole of the Earth is TRUE?

A. Its location never changes.

B. It corresponds to the N-pole of a bar magnet.

C. It corresponds to the S-pole of a bar magnet.

D. It is at the same location as the geographic north pole of the Earth

Ans: C. It corresponds to the S-pole of the bar magnet.

-The Earth’s magnetic field is made by swirling motion of molten iron in Earth’s outer core. The Earth’s North-magnetic pole is actually a south geographic pole as evidence by the needle of the compass.

2. An iron nail can be turned into a temporary magnet if it is held in a strong magnet field. Which method of magnetization is this?

A. Charging

B. Conduction

C. Introduction

D. Saturation

Ans: C. Introduction

-If you hold a bar magnet near or in contact with an iron nail, the nail becomes a magnet by induction. The nail retains its magnetism as long as the magnet is held near it or in contact with it but loses its magnetism as soon as the magnet is removed. Magnetism produced in this manner due to the presence of a magnet is called induced magnetism. During magnetic induction, nearer end of the magnet substance has opposite polarity and the farther end has similar polarity.

3. Which of the following factors affect the size of the induced current in a coil?

I. Number of turns in the coil

II. Size of the inducing field

III.Direction of the winding in the coil

IV. Resistance of the wire in the coil

A. I and II only

B. III and IV only

C. I, II, and III only

D. I, II, and IV only

Ans: D. I, II, and IV only

-When a magnet is moved towards a coil of wire, a current induced inside the wire. The size of the induced current is affected by using a stronger magnet, moving the magnet at a faster speed, using more turns of wire on the coil, and resistance of the wire in the coil.

4. To use the right hand rule to predict the direction of n induced current in a coil, your thumb must point__________________.

A. to the direction of the motion of the wire

B. to the S-pole of the induced magnetic field

C. in the direction of the induced current

D. in the direction of the inducing field

Ans: A. To the N-pole of  the induced magnetic field

-Right hand rule can be used to predict the direction of the induced current. Hold the thumb and first two finger of your right hand at right angle of each other. Point your first finger in the direction of the magnetic field and your thumb in the direction of motion of the wire. Now, your second finger points in the direction of the induced current.

5. When a bar magnet is inserted into a coil, a current of 12.0 A is induced in the coil. If four magnets of the same type are inserted into a coil at the same time, what would be the induced current?

A. 3 A

B. 4 A

C. 12 A

D. 48 A

Ans: D. 48 A

-Induced current= 12A x 4 magnets = 48 A

6. Which of the following involves adsorption?

A. Plating the copper on a steel object

B. Adherence of paint to wood surfaces

C. Brown color of the eyes of the Filipinos

D. Remobal of odor inside a refrigerator using charcoal

Ans: D. Remobal of odor inside a refrigerator using charcoal

-adsorption is the process that occurs when gas or liquid solute accumulates on the surdace of a solid ar liquid (adsorbent), forming a molecular or atomic film. Activated carbon, also called activated charcoal is a material with an exceptional high surface are.

7. Which of the following BEST describes temperature?

A. Temperature measures the total energy in something.

B. Temperature measures the kinetic energy in substance.

C. Temperature measures the total kinetic energy contained in an object.

D. Temperature measures the average molecular kinetic energy in substance.

Ans: D. Temperature measures the average molecular kinetic energy in substance.

-Temperature is a measure of the average kinetic energy of the particles of a substance. For instance, if most of the particles of air in your kitchen are moving faster than most of the particles of the bedroom as manifested by smelling quickly what your mother is cooking, then , the temperature of the air in your kitchen is higher than the air in the bedroom.

        

8. What is the direction of a magnetic field within a magnet?

A. From north to south

B. From south to north

C. Front to back

D. Back to front

Ans: A. From north to south

-Magnetic fields are continues and unbroken, forming closed loops. Magnetic field lines are defined to begin on the north pole of the magnet and terminate on the south pole.

9. Which is the induced voltage across a stationary conductor in a stationary magnetic field?

A. Decreased

B. Increased

C. Zero  

D. Reversed in polarity

Ans: C. Zero 

-For the voltage induction, either conductor or magnetic field should be in motion so that liked flux can change continuously to result voltage induction. Hence, voltage induction is zero.

10. What is the magneto motive force (mmf) of a wire with 8 turns carrying 3 A of current?

A. 2. 67

B. 24

C. 240

D. 2400

Ans: B. 24

-mmf = 8 turns x 3A = 24

11. A coil of wire is placed in a charging magnet field. If the number of turns in the coil is decreased, what will happen to the voltage induced across the coil?

A. Remain constant

B. Be excessive

C. Decrease

D. Increase

Ans: C. Decrease

-Any change in the magnetic environment of the coil of the wire will cause a voltage to be induced in the coil. The number of turns in the coil will have an effect on the amount of voltage that is induced into the circuit. Decreasing the number of turns on the rate of change of magnetic flux decreases the amount of induced voltage.

12. Which of the following is TRUE about the frequency and velocity of electromagnetic waves?

A. Frequency and wavelength  are interdependent of each other

B. As frequency increases, wavelength decreases

C. As frequency increases, wavelength increases

D. Frequency is constant for all wavelengths

Ans: B. As frequency increases, wavelength decreases

-There as a simple relationship between the wavelength and frequency of a particular electromagnetic wave and speed of light. In equation: c=v whereas: c=speed of light, = wave length, and v=frequency. It means that as frequency increases, the wavelength decreases.

13. Which of the following correctly lists electromagnetic waves in order form longest to shortest wave length?

A. Television, infrared, visible light, X-rays

B. Gamma rays, ultraviolet, infrared, microwaves

C. Radio waves, infrared, gamma rays, ultraviolet

D. Micro waves, ultraviolet, visible light, gamma rays

Ans: A. Television, infrared, visible light, X-rays

-Wavelength is the distance between one wave crest to the next. Electromagnetic waves differ from each other in wavelength. From longest to shortest, electromagnetic waves are arranged as follow: radiowaves, television, microwaves, infrared, visible light, ultraviolet, x-rays and gamma rays.

14. An electromagnetic wave is radiated by a straight wire antenna that is oriented vertically. What should be the orientation of a straight wire receiving antenna?

A. Diagonally

B. Vertically

C. Horizontally and in a direction parallel to the wave’s direction of motion

D. Horizontally and in a direction perpendicular to the wave’s direction of motion

Ans: An electromagnetic wave is radiated by a straight wire antenna that is oriented vertically. Such a wave could be best detected by a loop antenna oriented with tha plane of the loop vertical and parallel to the velocity of the vector wave.

15. What should a good diode tested with an ohmmeter indicate?

A. High resistance when forward or reverse biased

B. Low resistance when forward or reverse biased

C. High resistance when reverse biased and low resistance when forward biased

D. High resistance when forward biased and low resistance when forward biased

Ans: C. High resistance when reverse biased and low resistance when forward biased

The internal circuiting of an ohmmeter has a voltage source connected to its leads when it measures resistance. The voltage can be used to bias a diode without connecting it to a circuit. When the positive side of the ohmmeter voltage source is connected to the P-material and the negative side to the N-material, the diode is forward biased. Their condition causes the diode to have low resistance.

16. Vacuum tubes in a radio transmitter are used to __________.

A. record programs

B. provide DC supply

C. generate high power radio waves

D. provide lighting inside the studio

Ans: C. generate high power radio waves

-Invented in about 1910, vacuum tubes were basic components for electronics throughout the first half of the century, which saw the diffusion of radio, television, radar, sound reinforcement, sound recording and reproduction, large telephone networks, analog and digital computers, and industrial process control.

17. Which material is the usual component of an anode?

A. Aluminum

B. Carbon

C. Copper

D. Nickel

Ans: Aluminum anode alloy provides more protection and longer than zinc. It will continue to work in freshwater and is safe for use in salt water. Aluminum is the only anode that is safe for all applications.

18. A metal spoon is placed in a cup filled with hot coffee. After sometime, the exposed end of the spoon becomes hot even without a direct contact with the liquid. What explains this phenomenon?

A. Conduction

B. Convection

C. Radiation

D. Thermal expansion

Ans: A. Conduction

-Conduction is the transfer of heat from one particle of matter to another by direct particle contact. The particles of hot coffee collide with the particle of the submerged end of the spoon. As the particles of the spoon absorb energy and vibrate more rapidly, the temperature of the spoon increases.

19. Which cause the warmth that you fell when you place your finger at the side of the flame of a burning candle?

A. Conduction

B. Convection

C. Radiation

D. Not enough information given

Ans: C. Radiation

-Radiation is the transfer of heat from one object to another without direct physical contact. Our fingers can feel the heat of the burning candle without touching the flame itself.

20. Which process of heat transfer happens by the movement of mass from one place to another?

A. Conduction

B. Convection

C. Induction

D. Radiation

Ans: B. Convection

-Convection is the transfer of heat energy in fluids through the bulk movement of matter from one place to another. When a mass of a fluid is heated up, for example when it is in contact with a warmer surface, its molecules are carried way and scattered causing that the mass of the fluid becomes less dense. For this reason, the warmed mass of fluid goes down (the low-kinetic-energy molecules displace the molecules in high-kinetic-energy states). Through this process, the molecules of the hot fluid transfer heat continuously toward the volumes of the colder fluid.

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