Physics 7 Lesson 30: Summary of Chapter III Electricity
1. Summary of theory Tóm
1.1. It is possible to electrify objects by rubbing
1.2. There are two types of electric charge
– Negative charge ( – ) and positive charge ( + )
Interaction between charges: the same type repels each other, different types attract each other.
Interaction between electrically charged objects: same name repels each other, different names attract each other.
1.3. Electrically charged object Vật
Positively charged objects lose electrons, negatively charged objects gain more electrons.
1.4. Electric current, power source
An electric current is a directional flow of electric charges.
A power source is a device that provides a long-term current to power tools for the tools to function properly.
– Each power source has two poles: negative (-) and positive (+).
– Current flows in a closed circuit consisting of electrical devices connected to the two poles of the power source by wires.
1.5. Conductors and insulators.
– Conductor ⇒ allows electric current to pass.
For example: Copper, silver, iron, acid solution…
– Insulator ⇒ does not allow current to pass.
– In metals the electrons escape from the atom and move freely in the metal and are called free electrons ⇒ Electric current in metal is the flow of free electrons moving in a direction.
1.6. The effects of electric current
1.7. Electrically charged object Vật
The charged object is Ampere (symbolized A), the potential difference is Volt (denoted V).
1.8. How to make an electrical circuit?
There are two ways to connect an electrical circuit, in series and in parallel.
1.9. Formula in series and parallel circuits
– Serial hook
In a series circuit, the current has the same magnitude at different positions of the circuit: \(I_1=I_2=I_3\)
The potential difference between the two ends of the circuit is equal to the sum of the voltages on each lamp: \(U=U_1+U_2\)
For a circuit consisting of two lamps connected in parallel, the main circuit current is equal to the sum of the bypass currents: \(I=I_1+I_2\)
The potential difference between the two ends of the lamps connected in parallel is the same and equal to the potential difference between the two common junctions: \(U=U_1=U_2\)
1.10. Safety rules when using electricity
Only do experiments with power sources with voltages below 40 V
Insulated sheathed conductors must be used.
A civil electrical circuit consists of two conductors, a “hot” wire and a “cold” wire. Between them there is a voltage of 220V and the cold wire is connected to earth at the generating station. so between the hot wire and the human body touching the ground to the civil electrical network and electrical equipment if you do not know how to use it.
When someone is electrocuted, do not touch that person, but immediately find a way to immediately disconnect the power switch and call an ambulance.
2. Illustrated exercise
2.1. Form 1: Determine the circuit with the light bulb on
Of the four experiments arranged as shown in Figure 30.3, which one corresponds to the closed circuit and the light bulb?
A closed circuit consists of conductive objects connected in series and then connected to the two poles of the power source.
⇒ Experiment of Fig. 30.3c) corresponds to a closed circuit and a light bulb.
2.2. Form 2: Determine the direction of the current
In the circuit diagrams of Figure 30.2 , which diagram has an arrow indicating the correct direction of the current?
Diagram 30.2c) has an arrow indicating the correct direction of the current: coming out from the anode and entering the negative pole of the power source in a closed circuit.
3.1. Essay exercises
Question 1: There are five 1.5V class power sources; 3V; 6V; 9V; 12V and two identical bulbs both write 3V. These two bulbs need to be connected in series to one of the five power sources above. Which power source is most suitable? Why?
Verse 2: Electronic watches (battery-powered, with rotating hands) work on what effect of electric current?
Question 3: Why do electrical wires often used to connect lights, fans, etc. have to separate the two cores?
Verse 4: Electric shock is caused by what effect of electric current?
3.2. Multiple choice exercises Bài
Question 1: A flashlight can withstand a maximum current of 0.5A. If a current of the following magnitude is passed through the lamp, which case will the light be the strongest?
A. 0.7A B. 0.60A C. 0.45A D. 0.48A
Verse 2: To galvanize a coil of steel, it must:
A. Soak the steel coil in a zinc salt solution and then heat the solution.
B. Connect the steel coil to the negative terminal of the power source, then dip it in the zinc salt solution and close the circuit to let the current flow through the solution for a while.
C. Immerse the coil in a zinc salt solution and then pass an electric current through this solution.
D. Connect the steel coil to the positive pole of the power source, then dip it in a zinc salt solution and let the current flow through the solution.
Question 3: The following conclusions are not correct?
A. Normally atoms are electrically neutral.
B. Each atom has a positively charged nucleus in the middle.
C. Electrons can be ejected from the nucleus of an atom to become a free electron.
D. Electrons are not stationary but move around the nucleus forming an atomic shell.
Verse 4: When rubbing an iron rod with wool, which of the following statements is true?
A. After rubbing, the iron rod becomes positively charged.
B. After rubbing, the iron rod becomes negatively charged.
C. After rubbing, the felt piece of wool becomes positively charged.
D. After rubbing, two electrically neutral objects are obtained.
Through this lecture Summarizing Chapter III: Electricity, you need to complete some of the objectives given by the lesson, such as:
Consolidate and firmly grasp the basic knowledge of Chapter 3.
Apply a synthesis of learned knowledge to solve problems (Answer questions, solve exercises, explain phenomena …) related.