8th grade physics problems

1.The current and voltage are reduced.

When the sliding rheostat is impeded, the total resistance in the circuit becomes larger, the power supply voltage remains unchanged, and the total current decreases. The current is equal everywhere in the series circuit, the current flowing through the bulb becomes smaller, the lamp resistance does not change, and the voltage at both ends decreases.

2.The current and voltage are reduced.

The whole circuit is connected in series, and the sliding rheostat is impeded, and the total resistance in the circuit becomes larger, the power supply voltage remains unchanged, and the total current becomes smaller. The current is equal everywhere in the series circuit, the current flowing through the bulb becomes smaller, the lamp resistance does not change, and the voltage at both ends decreases.

3.The bulb in series with the sliding rheostat is dimmed and the other bulb is unchanged.

The sliding rheostat is connected in series with one of the bulbs, and the sliding rheostat is impeded, and the resistance in this branch becomes larger, the supply voltage remains the same, and the total current becomes smaller. The current is equal everywhere in the series circuit, the current flowing through the bulb becomes smaller, the lamp resistance does not change, and the voltage at both ends decreases. The voltage at both ends of the other bulb remains the same, always equal to the mains voltage, and the current is also constant.

4.The current and voltage are unchanged.

The sliding rheostat and the two lamps are connected in parallel, the voltage at both ends of the lamp is unchanged, which is always equal to the power supply voltage, the resistance of the lamp is unchanged, and the current is also unchanged.

1.The current of the two bulbs decreases, and so does the voltage.

2.The current of the two bulbs decreases, and so does the voltage.

3.The individual bulbs do not change, and the current and voltage of the bulbs connected to the rheostat are reduced.

4.Neither bulb changed.

1.Decrease The sliding rheostat increases the resistance, resulting in a decrease in the current, while the lamp resistance does not change, so the voltage decreases.

2.Decrease The total resistance of the two bulbs remains unchanged, and the resistance of the sliding rheostat causes the current to decrease, resulting in a decrease in the current on the branch, so the current of the two bulbs decreases, and the voltage also decreases.

3.The bulb in series with the sliding rheostat has a reduced current and a reduced voltage;The bulb voltage on the other branch does not change, and the current does not change.

4.No change. The circuit divides the voltage in series and shunts in parallel.

1. Make it smaller. 2. No change.

3. It is darkened in series with it, and the other remains unchanged.

4. No change.

1. The point pressure of the two lamps decreases, and the sum of the decreasing values is equal to the slip increase value, that is, δU1 + δU2 = δu slip;Second, the current and voltage are all smaller, and δu1=δu2=δu slip;3. The one that is connected in series with the slip becomes smaller, and the other constant δu lamp (the one of the string) = δu slip;Fourth, unchanged. The resistance is regarded as one, and it is considered according to the series voltage division, parallel current distribution, and each branch does not affect each other.

1.Both the current and the voltage become smaller.

2.Both the current and the voltage become smaller.

3.The voltage and current of the bulb in series with the sliding rheostat decreases, the other does not change.

4.Both the current and the voltage are constant.

1. Prevent water evaporation.

2. When slowly hazing on the hand, the temperature of the water vapor is higher, and the temperature of the palm is lower, the water vapor will liquefy on the surface of the palm when it is cold, and the liquefaction will be exothermic, which is the hand will feel warm. Blowing your hands will increase the velocity of the air above your palms, speeding up the evaporation of sweat or droplets in your palms, which will absorb heat and make your hands feel colder.

1.Slows down evaporation.

2.In winter, the hand Ha gas liquefies on cold hands, and liquefied and heat-released hands will feel warm. If you blow your hands, it will speed up the evaporation of the sweat glands on the surface of your hands, and the evaporation will absorb heat and feel colder.

1.In order to prevent the water of fruits and vegetables from evaporating, so that fruits and vegetables can achieve the purpose of freshness. Because there are three factors that affect the evaporation of liquids:

The temperature of the liquid, the area of contact between the liquid and the air, and the flow of air on the surface of the liquid. The temperature in the refrigerator is low, the air flow is slow, and the cling film reduces the contact area with the air, so the water evaporates very slowly, achieving the purpose of preservation.

2.In the first case, the water vapor exhaled from the mouth liquefies when it encounters the cold hand and is exothermic, and the hand absorbs the heat and feels warm. In the second case, the rapid air flow from the mouth is the acceleration of the evaporation of the liquid such as sweat on the hands, and the hands feel cold after absorbing more heat in one unit of time.