Physics questions in the second year of junior high school Physics questions in the first semester o

Connect the two resistors in series into the circuit, connect the voltmeter in parallel at both ends of the resistor RO, measure the voltage falling at both ends of the RO, and then divide the voltage by the resistance of the RO to find the current of the series circuit. Then connect the voltmeter in parallel to the two ends of the unknown resistance Rx, measure the voltage falling on both ends of Rx, divide the voltage at both ends of Rx by the current, and get the resistance value of Rx.

Expression: i=u1 ro

rx=u2 i=u2 (u1 ro)=(u2 u1)ro, I don't know if I'm clear enough).

1.Connect the two resistors and the power supply in series into the circuit, connect the voltmeter in parallel at both ends of the resistor RO, and connect the switch in parallel with the RX. (Circuit diagram to do by yourself).

2.The switch is closed first, and the voltage that falls on both ends of the RO is measured and recorded as U, that is, the power supply voltage.

3.Disconnect the switch and read out the voltmeter's indication as U1.

Then the voltage at both ends of the rx is u-u1 and the current is u1 ro.

Expression: rx=(u-u1)ro u1

The voltmeter is connected to rx, first adjust the position resistance to the maximum, and note the voltmeter v1, so the current is v1 rx, then the voltage of r0 is 3-v1, and the passing current is (3-v1) r0, and the current is the same, because the current is the same, there is an equation v1 rx=(3-v1) r0

The positive pole of the battery pack ——— switch ---R0---Rx--- negative pole (series)1, connect the voltmeter in parallel with RO first, measure the voltage as UO, and use Ohm's law to obtain i=uo RO

2. Then connect the voltmeter in parallel with Rx, and measure the voltage as UX, because the series current is equal, so use Ohm's law to get RX=UX I=UX

uo/ro

<>2.The voltage of R0 is measured, and the voltage is divided by R0 to obtain the current i of the series circuit. Then connect the voltmeter to both ends of the Rx, measure its voltage, and divide it by the current I

There are two scenarios;

Bicycles pass through the sedan first; T car = s v = [v car = 54km h = 15m s].

t self = t car = v bike = s t = [

The sedan Tan Jian passed the bicycle first and then passed; t-car = s v=[t self=t car = v bike =s t=

Answer; Larger than Lixinqing anterior limb less than 2m s

1: Quantitative: the same milk bottle, the same milk, the same milk quality...

Variables: Environment...

2 : Through experiments, it can be concluded that water has good thermal conductivity (because the specific heat capacity of water is large, who can quickly absorb the heat from the walls of the milk bottle and disperse it into the air).

1) The two milk bottles should be the same, and the same amount of milk should be poured in.

The quality is the same, the height of the pad is the same.

The air has good thermal conductivity.

1) The amount of milk is the same, and the flow speed of the air above the milk is the same.

2) The thermal conductivity of the air is good.

1.The following objects that are not light sources are (b.).Moon.

a.Sun. b.Moon.

c.Fireworks set off.

d.A glowing electric lamp.

2.The sun's rays are at an angle of 40° to the horizontal plane, and for the reflected rays to propagate to the right in the horizontal direction, the plane mirror should be at an angle of 20° to the horizontal plane

3."Sundial"

Immediately"They are all methods (or) instruments used by the ancients to observe the hours, which take advantage of the nature of the linear propagation of light.

4.The light is emitted from a vacuum onto a flat transparent material, and the angle between the reflected and refracted rays is b. Then the following statement is correct (a.).When A=30°, the range of the B angle is between 120° and 150°.

a.When A=30°, the range of the B angle is between 120° and 150°.

b.When A=30°, the B angle may be greater than 150°

The angle will increase with the increase of the A angle, but the maximum will not reach 180° The maximum size of the sock will decrease with the decrease of the A angle, and the maximum will not reach 180°