问题 选择题

如图(a)所示,一矩形线圈abcd放置在匀强磁场中,并绕过ab、cd中点的轴OO′以角速度ω逆时针匀速转动.若以线圈平面与磁场夹角θ=45°时[如图(b)]为计时起点,并规定当电流自a流向b时电流方向为正.则下列四幅图中正确的是(   )

答案

选D.

t=0时,由右手定则得,此时ad中电流方向为由a到d,与规定的正方向相反,电流为负值.又因为此时ad、bc两边的切割速度方向与磁场方向成45°夹角,由E=2Blv,可得E=2×Blv=Em,故电流是最大值的,A、B均错.线圈在接下来45°的转动过程中,ad、bc两边的切割速度越来越小,所以感应电动势应减小,感应电流应减小,因此C错D正确.

多选题
单项选择题

Social control refers to social processes, planned or unplanned, by which people are taught, persuaded, or forced to conform to norms. In every society, some punishments or negative sanctions are established for deviant behavior. Without deviant behavior there would not be need for social control and without social control there would not be a way of recognizing the boundary between the acceptable and the unacceptable.

Social control may be either formal or informal. Informal mechanisms include expressions of disapproval by significant others and withholding of positive rewards for disapproved behavior. Most people internalize norms in the course of socialization. This is any group’s most powerful protection against deviance, in that the individual’s own conscience operates as an agent of social control. When informal sanctions fail, formal agents of social control may be called upon. In contemporary society, such formal agents and agencies include psychiatry and other mental health professions; mental hospitals; police and courts of law; prisons; and social welfare agencies. All these formal agents function to limit, correct, and control violation of norms. Conflict theorists would also point out that social control agents and systems tend, in any society, to serve the interests of powerful groups and to enforce the norms most beneficial to those who make the rules and who, therefore, define unacceptable behavior.

Social control, whether formal or informal, has a dual function. First, it punishes the wrongdoer and reaff’irms the boundaries of acceptable behavior. Second, and less recognized, it regulates the manner in which deviants are treated.

Which statement about social control agents is NOT true().

A. They tend to serve the interest of those who enforce the norms.

B. They tend to serve the interest of those who receive a benefit.

C. They tend to serve the interest of those who make the rules.

D. They tend to serve the interest of those who are powerful.