Latest Physical Science Reviewer 8

1. When coal is burned to produce electricity, the electrical energy produced is less than the potential energy of the coal. Which BEST explains this observation?

A. The amount energy in the coal is not known.

B. As the coil is heated, the molecules move so fast that they are destroyed.

C. Some of the potential energy in the coal is converted into forms of energy other than electricity.

D. Some of the potential energy in the coal requires more intense heat so that can be compared to electricity.

Ans: C. Some of the potential energy in the coal is converted into forms of energy other than electricity.

-There are multiple steps in converting coal into electricity. In each step, energy transformations occur that’s why the electrical energy produced is less than the potential energy of the coal.

2. What is the TRUE of all combinations of resistors arranged in parallel?

I. Current spilts down each leg of the combination.

II. Voltage is constant across each leg of the combination.

III.Resistance is the same for each leg of the combination.

A. I and II only

B. I and II only

C. II and II only

D. I, II and III

Ans: A. I and II only

-A parallel circuit has more than one path for current to flow. In parallel circuit, the total current that flows through the circuit is equal to the sum of the currents in the separate resistance; the potential drop in each resistor is the same as the magnitude of the applied electromotive force; and the reciprocal of the total resistance is equal to the sum of the reciprocals of the separate resistances.

3. What is the closed, continuous path through which electrons can flow?

A. Charge

B. Circuit

C. Resistor

D. Voltage

Ans: B. Circuit

-A circuit is composed of electronic components connected by conductive wires through which electric current flow. A charge is a property of matter that causes it to experience a force

4. What will be your charge if you scrape electrons from your feet while scuffing across the rug?

A. Negative

B. Neutral

C. Positive

D. Not enough information given

Ans: C. Positive

-You lose electrons from your feet when you cross a rug, you become positively charged.

5. How will you force charge if the distance between the two charge spheres is doubled?

A. The force is doubled.

B. The force is tripled.

C. The force is quadrupled.

D. The force is multiplied eight times.

Ans: C. The force is quadrupled.

-Coulomb’s Law states that the size of the force varies inversely as the square of the distance between the two charges. Therefore, if the distance between the two charges is doubled, the attraction or repulsion becomes weaker, decreasing to one-fourth of the original value.

6. A 6 ohm and 12 ohm resistors are connected in parallel with each other to a battery. Which of the following is TRUE?

A. More current will flow through the 20 ohm resistor.

B. The current flowing through the resistor is the same.

C. The resistor values must be equal for the circuit to work.

D. The potential difference across the two resistors is the same .

Ans: D. The potential difference across the two resistors is the same .

-Voltage is the same across each component of the parallel circuit.

7. A new 1.5 V dry cell furnishes 30 A when short-circuited. Find the internal resistance of the cell.

A. 0.05 Ω

B. 0.10 Ω

C. 1.5 Ω

D. 30 Ω

Ans: A. 0.05 Ω

-E = I/R           R = E/I        R = 1.5 V/30        A = 0.05 Ω

8. If three identical lamps are connected in parallel to A 6 V dry cell, what is the voltage drop across each lamp?

A. 2 V

B. 3 V

C. 6 V

D. 18 V

Ans: C. 6 V

-In a series circuit, any current that flows through one bulb must go through the other bulbs as well, so each bulb draws the same current. The voltage drop across each bulb is the same.

9. Which of the following describes an electric current?

A. Regulates the movement of electric charge

B. The opposition material offers to the electron flow

C. The electric pressure that causes charged particles to flow

D. The movement of charged particles in the specific direction

Ans: D. The movement of charged particles in the specific direction

-An electric current is a flow of electric charge…..

10. A 10 W bulb and a 20 W bulb are connected in a series circuit. Which bulb has the more current flowing in it?

A. The 10 W bulb

B. The  20 W bulb

C. Both bulbs have the same current

D. Cannot be determined

Ans: C. Both bulbs have the same current

-See number 148 for the explanation.

11. Which of the following are characteristics of a series circuit?

I. The current that flows through each resistance is the same as the total current throughout the circuit.

II. The sum of all the individual voltage drops in the same as the applied voltage.

III. The reciprocal of the total resistance is equal to the sum of the reciprocal of the separate resistances.

IV. The voltage drop in each resistance is the same as the magnitude of the applied voltage.

A. I and II only

B. I and III only

C. III and IV only

D. I, II, and III only

Ans: A. I and II only

-A series circuit has two or more loads but current flows through a single conducting path. In this circuit, the current that flows through resistance is the same as the total current throughout the circuit; the sum of all the individual voltage drops in the same as the applied electromotive force, and the total resistance is equal to the sum of the individual resistances.

12. Which states that the sum of all potential rises and potential drops in any loop (closed circuit ) is zero?

A. Coulomb’s Law

B. Kirchoff’s Law

C. Law of Electrolysis

D. Ohm’s Law

Ans: B. Kirchoff’s Law

-Kirchoff’s Law state that the total current or charge entering a junction or node is exactly equal to the charge leaving the node as it has no other place to go except to leave, as no charge is lost within the node. It simply means that the algebraic sum of all the currents entering and leaving a node must be equal to zero.

13. A television and an electric fan are connected in parallel top a 220 V line. The current in the television is 8 A and in the electric fan is 3 A. What is the current flowing in the line?

A. 2.67 A

B. 5 A

C. 11 A

D. 24 A

Ans: C. 11 A

-I_T = I₁ + I_2… I_n

 I_T = 8 A + 3 A = 11 A

14. What happens to the current if resistance increases?

A. Decreases

B. Increases

C. No change

D. Cannot be determined

Ans: A. Decreases

-Ohm’s Law state that the current is directly proportional to the voltage and inversely proportional to the resistance. It means that if resistance increases, current decreases.

15. Which of the following statement DOES NOT represent Ohm’s Law?

A. Current/potential difference =constant

B. Potential difference/current = constant

C. Potential difference = current x resistance

D. Current = resistance x potential difference

Ans:  D. Current = resistance x potential difference

-Ohm’s Law in equation form is I=V/R whereas: I= current, V=voltage, R=resistance. From this equation, V=IR and R = V/I.

16. 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.

17. What is the resistance of an electric bulb drawing 1.2 A current and 6.0 V?

A. 0.2 Ω

B. 0.5 Ω

C. 2 Ω

D. 5 Ω

Ans: D. 5 ohms

-R=V/I    R= 6V/1.2 V= 5 ohms

18. What happens to the current-carrying ability of a wire as temperature increases?

A. There is no change.

B. The wire can’t carry any current.

C. The wire can carry more current.

D. The wire can carry less current.

Ans: D. The wire can carry less current.

-Resistance increases with increase in temperature so the current-carrying capacity of the wire decreases.

19. A 300 W at 220 V TV set is used at an average of 4 hours a day for 30 days. If the electrical energy costs Php 1.60 per kilowatt-hour, how much is the energy cost?

A. Php 5.76

B. Php 22.50

C. Php 57.60

D. Php 225.00

Ans: C. Php 57.60

-W= P    T

 W= (0.30 kW) (4hrs x 30 days)

 W= 36 kWh

 Cost = (36 kWh) (1.60/kWh)

          = Php 57.60

20. Electromagnetic radiation can be used for wireless communications. Which of the following can be used to transmit signals such as mobile phone calls?

A. Infrared

B. Gamma

C. Microwaves

D. Radiowaves

Ans: C. Microwaves

-Mobile phones communicate with their base stations using low-intensity microwave radiation. Microwaves can be used to transmit information over large distances, although some areas have poor signals. Other digital wireless system, such as data communication networks, produce similar radiation.

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