Do I need to take a Ham radio exam to use it? Is there any radio that I can use for emergency which has powerful broadcast range over 4miles & I don't need a license to carry it.

You dont need a license to cary it or receive on it. You also don't need a license to transmit in an emergency situation. You only need a license for non-emergency transmissions.

Brian, while your response is technically correct, I think it is hardly the most responsible way to approach the problem. One should never rely on untested equipment in an emergency. In the case of radio communications, it is a simple process to obtain a small amount of knowledge. Your response could encourage people to purchase amateur radio gear without obtaining the knowledge to use it effectively.

But to cover a 4-mile range does not require a particularly powerful, or even license-required radio. CB radio, legally limited to 4 watts transmit power, does not require licensing. GMRS radios, which are approved up to 5 watts for handheld transceivers, require only a license fee rather than a test.

In an emergency, especially one such as Hurricane Katrina, where there is widespread infrastructure damage, radio communications may be the only available means of long-distance communications, and the available bandwidth will be heavily taxed. A little knowledge goes a long way in helping get a message out to the right people at the right time.

Brian merely stated the facts. He didn't encourage them to do that.

where can I study to get license to use these amatuer radio? Is it expensive to get license? Is it available in Canada? I am living in Canada

Picard, try here: http://www.rac.ca/ That's Radio Amateurs of Canada, sort of the Canadian version of the ARRL.